An atheist is someone who doesn't believe in any god. You can break it down by etymology: a(without)theist(god). We can go into Leddit distinctions between different kinds of atheists, like those who positively assert the non-existence of gods vs those who are merely skeptical enough of them to not think they're real given the information they have, but I don't think it's really germane to this conversation, beyond this point:
The conversation is what does foxhole prayer entail. I don't think it entails the existence of God. I do think it's an indicator that the atheist in question is not very confident in their atheism, that they become pliant to theism in dire circumstance. It's a statement on the personality and views of the person foxhole praying. It's not a statement on external, objective reality. Quite a few believers lose their faith given hardship or the fear of imminent death. This is a two way street.