I trust Paul implicitly, and I suspect most YC Founders do, and that probably has a lot to do with the acceptance rate. I wasn't in the meeting obviously, so I can't know how I would have reacted to the specifics, but I can say knowing only what I know now I probably would have at least taken the weekend to do my homework.
Edit: phrasing.
What rational reason would an angel investor have to avoid investing in a company that has taken this investment?
Actually, the TC article says many of them signed papers at the offer meeting itself.
I understand the offer sounds fantastic, but surely they'd want some advice first?
Obviously they didn't, but it seems a little rash.
(Or he might die of a heart attack, or the Russian government might seize his assets, or any number of other unlikely scenarios might make him unable to close the deal.)