The amount is small, but is that not an indirect way of showing interest in Bitcoin for someone like Peter who speaks ill about Bitcoin each time he has the opportunity?

I think he is seeking for more attention using the growing popularity of Bitcoin. The donation drive achieves a dual purpose: an extra cash and a form of mockery to Bitcoin maximalists who promote the Bitcoin all the time on X. You never know, some may actually want him to adopt and start using Bitcoin since he is quite an influential person.
Provably it is since if he's going to be a critic of Bitcoin then he will make his name controversial since people will always talk about him and try debate him with what he believe.
But for asking BTC on his Birthday? That's quiet pathetic action on his side since how could he ask that one if he's really a Bitcoin critic. Maybe he just using that situation to fool people and grant his request once he do this kind of action. I remember that Justin Sun give Warren buffet a samsung phone loaded with 1 BTC and Tron. Maybe this is what Peter Schiff want to replicate if there's rich man will offer him such nice deal just like what Sun did.