It's possible that it's just because it was literally called "Bitcoin Wallet", an exact match for your search, or boosted by fake reviews, or it was actually an ad that you didn't notice. Though it shouldn't have gotten past review at all
But I don't really understand why you'd blindly trust some random app?
Also, would be interesting to take a look at the app, sadly know nothing about ios apps or how to get the IPA, only android.