Why was asking Reddit a mistake?

Put yourself in the OP's shoes. You're a college student and you get a notice like this handed to you. It's not like you have an IP lawyer on retainer or cash to run out and hire one instantly.

In fact, one helpful redditor pointed out that his college might have a law school that would be willing to help with his case as a teaching exercise. I bet the OP knew nothing about that, and that's worth the price of visiting reddit alone.

Simple. It was a mistake because it looks like the kid would accept the offer if it was larger. Go to an IP lawyer and watch dollar signs pop out of their eyes. In a case like this, they'll assist with negotiating a fair price on contingency. If the kid really doesn't want to sell, he can go to EFF or get a lawyer to do this pro-bono. They love this sort of David vs Goliath stuff.

How would he know that an IP lawyer would be eager to take the case? Is that supposed to be common sense or something?

You're suggesting an IP lawyer would take the case on a no-cure, no-pay basis? Why is your HN advice more credible than the Reddit advice? Are you a lawyer? Have you dealt with this situation? Or are you in fact armchair lawyering as much as the Reddit commenters?

I asked my wife, who is an IP lawyer. That was her advice. Of course, you would expect a lawyer to recommend to see another lawyer, but in this case, it makes sense since there's $$$ involved.

I don't know about in the US, but a lot of UK universities will have a pro-bono law team that will help students with legal problems (run by professors but with law students in observance so they can get some "real" world experience).