What deal? Being X made no deals. The moral of that short encounter seemed to be that Being X wanted to give proto-Tanya a chance to develop faith as proto-Tanya explained why he didn't have any need for it. At least if that wasn't the purpose, I don't know what it was. What's the point of making the dude repeat a successful life with no need for faith right after he was told he won't get reincarnated?

Saying Being X couldn't control it or it was a mistake... Right. Why bother writing such a story in the first place?