I think Macdonough was smart to offer $100 or the opportunity to learn to code. It was a good way to screen out unmotivated people -- if someone is homeless and turns down $100, it's likely that that they're very motivated.
Of course not, that's silly. We are discussing within the context of homelessness, in which the guy is playing a game with a vulnerable individual by offering an amount that is far higher than a change, but far lower that any developer (even junior) would consider an offensive offer for a mobile app.
I don't think you have the story straight. Patrick didn't get free labor, he taught Grand so he could create his own app (and maybe profit).
Since $100 has a higher marginal utility for a desperately poor homeless person than most people with adequate shelter, the fact that someone turns it down shows an uncommon amount of motivation.
But really, if you're going from what I said to "root causes of homelessness", I can't help but feel you're just looking to pick an argument.