I would say that race plays another factor as well. Sorry if this has been mentioned. I think it is pretty obvious that part of the reason that the guy wasn't drafted, not noticed, etc. is because he "just doesn't look like an NBA player," and much of that is because of his race. It isn't racist, it is just the way it is, when these GMs see player after player develope or flop in the league they develop an image of the kind of player that they believe will succeed. A thin (though he isn't rail thin), 6'3 Asian dude with a mediocre jumper isn't going to wow scouts. Sometimes though there are players who "break the mold," Lin happens to be one of them.
So there is the race factor above and then the novelty of the 'unknown guy from Harvard who was living on his bros couch who came out of nowhere to do spectacular things in his first few games in the league. AND ITS IN NY, AND HE'S ASIAN.
Tbh, when I first heard of him after his (not really a debut) debut game was, "Jeremy Lynn <--- notice the spelling eh, must be some white dude who threw down a nasty dunk or something.