I don’t think this is right. The idea seems to be that his post-game interview shows he didn’t understand the positions very well despite playing them accurately, so he may have cheated. But a) today there was a huge amount of extra security and specific scrutiny on him, b) he drew despite having a substantial advantage at one point, and c) a bad interview where he fumbled some stuff would be a nothing-burger if it hadn’t come after an accusation. It seems much more likely that this is a swirl of confirmation bias, not sound adjustments to priors. No one seemed to think his play was suspicious before the Magnus tweet and now everyone is reading tea leaves.

The point is that people keep bringing his post game interview today which is only relevant if he cheated in today's game, when security and scrutiny were at their highest.

So called Bayesian analysis frequently goes awry because of its ultimate dependence on assumptions (priors). But you don't even bother to do a calculation.

Seems ironic to ask this on a post where a guy's cheating device malfunctions causing him to lose. There could be limitations which prevent him from cheating completely accurately

I don't know about his game yesterday with Firouzja, but the rumor is that Magnus thinks Niemann got hold of his opening preparation before the game, which would put him at a huge advantage.

This is not the point. The point was that he good enough to nearly beat the #4 in the world if he wasn't cheating.