For the second paragraph: Imagine a man warped out of the past somewhere into the future. His clothes look funny and any interaction he makes with people draws an odd response. Some give him money, some people say "no thank you" for some reason, and so on. He can test this, he can see that nearly everyone behaves this way. So he assumes this is simply how people here behave.
Later on, something happens that forces him to wear clothes like everyone else is wearing. And how people react to him changes completely. All his testing proved that people react one certain way, but he didn't understand why so he didn't realize what his testing had showed was actually just a small subset of the actual behavior and was actually an extremely rare case.
I really like your comment, and I really wish to reply with a video with a Louie CK stand-up comedy piece about a lion and a giraffe. But I'm not sure if I can post the link here.
The second paragraph was me trying to, very briefly, sum up the consequences of positivist epistomology. The alternative that Chomsky proposes is that observational knowledge can only describe the things that are true given the process that generates the interactive behaviors we observe. This applies to everything from humanities and linguistics to physical interactions (which is why people have such difficulty explaining quantum physics). Consider, for example, the idea that computers think in zeros and ones: it is usually plenty accurate, even though it is really an abstraction of high/low voltage signal. But if we encounter random bit flips it may be helpful to know that actually we are working with high/low signal and so a cosmic ray interacting with our RAM could produce a flip. Equally, we write programs in higher level languages without worrying that loops aren't an inherent property of the computer. "Loops" aren't a lie, but they also aren't a fact: they are useful knowledge.
Most knowledge falls into this area, of being the product of current, generative interactions. In this world it is possible to say that some statement isn't supported by evidence, so we can still have science based on falsifiablity. We can even fully describe the observed behavior of some system under a set of conditions. That knowledge is likely to be useful, even. But it is incomplete, and shouldn't be elevated to a place of infallible "fact" lest we miss the additional capabilities we might acquire by manipulating those assumptions.
Thanks. Your summary was eloquent, but I'll have to read the article as well to make sure I understand correctly. What strikes me is that Alfred Korzybski spoke about those same issues (and much more) in his 1933 book called "Science and Sanity" (well worth a read, although bare in mind it took me several years to finish it). So when Chomsky wrote his stuff, Korzybski had already addressed this very comprehensively.
As for the second paragraph, I completely do not understand what it means.