No, they're not. "Good guys" don't fire someone without a severance after 2 weeks for no reason, especially not after you've put your reputation on the line as you have.

I let all job offers go (I had a few good ones)

Try to get those offers back. Explain what happened. If there's another solid option you can take, then you don't need to worry. Try to get a month or two of severance from the YCs but don't worry too much if you can't, and don't jeopardize success in your next gig by putting your energies into an all-out legal fight. If you're turned down, however, document it. This is going to help you make a case against the YC founders. The words you want are detrimental reliance, and to make that case, you need to establish damages. A job offer you had, that you lost, constitute damages. You relied detrimentally on the offer (later rescinded) from the YC company. That's a stronger case to make than wrongful termination, which often involves venturing into the undefined behavior of at-will employment.

Then-- if you can't get a severance on the order of 3-4 months, plus reimbursement for any relocation (both ways) or visa costs you've-- get a lawyer involved and sue.