Regardless of the semantic discussion on what exactly a 'blockchain' is and whether or not this qualifies, I found the article interesting by taking a tiny piece of the whole monster and demystifying it a bit.
I don't see this any differently than a tutorial that makes a static image move around the screen with key presses. Is it a full game? Not at all. But can it teach you how to build a tiny piece of it, and you can look at other tutorials to figure out how to build other tiny pieces of it, and eventually synthesize that knowledge and make a full game? Yes.
The clever part about bitcoin is reusing existing technologies in a novel way.
It uses:
- Hashcash-style proof of work: http://www.hashcash.org/ (originally designed to make spamming harder, although I don't think it ever really became widely adopted).
- When a new "node" connects to the network it uses hardcoded addresses and DNS seeds to find other nodes to connect to: https://bitcoin.org/en/glossary/dns-seed (before that it used IRC)
And there are probably a few other things but basically if you know how to work with those technologies then you have all the tools you need to implement a bitcoin clone. It's nothing groundbreaking, it's "just" a clever novel use of existing technology.
All the actual "rules" of the network (the block reward etc...) are simply validated in the nodes, they'll reject any block that's not properly crafted (i.e. bad reward, invalid proof of work etc...). Therefore the node consensus dictates what bitcoin is. If you implement a non-compatible change in the client and you don't convince all the other users to switch you create a fork since you won't have the same definition of what constitutes a valid block.
I don't see this any differently than a tutorial that makes a static image move around the screen with key presses. Is it a full game? Not at all. But can it teach you how to build a tiny piece of it, and you can look at other tutorials to figure out how to build other tiny pieces of it, and eventually synthesize that knowledge and make a full game? Yes.