I'm on the fence about that one. I used to sell licensed software and of course I lost plenty of money due to piracy (if a prospect cancels a sale but turns out to be running the product after all I think that qualifies ;)). Piracy is illegal (of software), but this case deals with source code. Now it is of course possible to see the name of the file and wonder 'hey, isn't that copyrighted software' but you could make that call for every package and you'd get a bunch of people arguing that the only way open source can function is by allowing people to download stuff, then verify the license is 'legit', compiling it and running it.
So there are good reasons for not criminalizing the downloading of code, and the responsibility of anybody that does download code is that they will deal with it in the proper way once they find out the terms. If the code says '(C) 2000-2007 Kaspersky Inc, NOT for distribution or resale' at the top (I made that up), you will probably have a good idea that it's not wise for you to proceed, if on the other hand it has an open source license as a rider and you can not find anything wrong with it after careful inspection you should be free to proceed.
To make an insightful decision you'd have to download it first.
It doesn't, because there's no transfer of anything here (well of the work itself, I mean of no legal thing, I'm not sure what the exact name in English is - "property right" or something I guess). There is no right on the work that is transferred by someone making a home copy; it's merely explicitly excluded from being an infringement on the author's copyright.
So the person doing to uploading isn't transferring anything of legal substance (which, if he doesn't have any rights on the work himself, can't, as you say).
Ok let me try again. In the following, 'Auteurswet' is the Dutch copyright law. Also, there are three parties in the example: 'the uploader', the one who provides the work and is assumed not to be entitled to do so (for the example); 'the downloader' who makes the copy; and 'the author', the holder of the copyright.
Also, 'nemo plus iuris' is an abbreviation of 'nemo plus iuris transferre potest quam ipse habet' which means 'nobody can transfer more than he has'. It's a cornerstone of property law which, in the context of physical goods but also of other property rights, means quite obviously that if you don't have rights to something, you can't transfer those rights to someone else. This may seem obvious but it comes into play when rights are retroactively discovered to have never existed at all (which is much more common than one might suspect; for example in cases of bankruptcy, non-payment with a reservation of ownership clause, ...). Then transfers of goods can be invalid and this has serious implications for purposes of ownership, repossession etc.
Anyway, back to the case at hand. First we need to distinguish between two things that can be transferred: the rights to the software, the 'copyright' (this is not a license, forget about 'licenses', it is the copyright itself.) and the software itself that is transferred. Because in English both are described by the word 'transfer' it is extra confusing; the copyright (can be but isn't in this case) 'transferred' ('overgedragen') in the same way a deed is transferred, while the software is merely 'transferred' ('gekopieerd', copied) over the wire. 'Transferring' a copyright needs to be done in writing (art 2 sub 2 Auteurswet), for example, 'transferring' some software over the internet doesn't, obviously.
Now then, the copyright is a 'property right' ('vermogensrecht'), and is with the author (in the case of the example). It is this 'copyright' that the nemo plus iuris sees to; and since 'the uploader' doesn't have it in the first place, he can't transfer it. Which makes sense.
Why then isn't the making of the copy covered by this nemo plus iuris? It's because there is no transfer of any property right going on at all. The downloader doesn't get a property right. The Auteurswet merely says that this specific making of a copy (for personal use, etc.; details are in artt 15 and 16 of the Auteurswet) is not a copyright infraction. That doesn't make the downloader holder of any copyright, or of any property right at all. And that is why the nemo plus iuris principle is not in play here.
I'm not normally one to complain about downvoting, but could whoever did so explain why, because it seems that each time I try to bring some legal facts into this whole discussion some people feel they need to express their dislike of reality by downvoting.
Because it is absolutely dense, inscrutable and grammatically incorrect legalese. According to my best effort to understand what you were writing in the comment was: "Downloading the sourcecode is not illegal, because no actual thing gets downloaded, and if the downloader then uploads the code, that cannot be illegal since he has no right to the software anyway." That makes no sense at all.
