This is a special post for quick takes by J Bostock. Only they can create top-level comments. Comments here also appear on the Quick Takes page and All Posts page.
Rather than using Bayesian reasoning to estimate P(A|B=b) it seems like most people the following heuristic:
Condition on A=a and B=b for different values of a
For each a, estimate the remaining uncertainty given A=a and B=b
Choose the a with the lowest remaining uncertainty from step 2
This is how you get "Saint Austacious could levitate, therefore God", since given [levitating saint] AND [God exists] there is very little uncertainty over what happened. Whereas given [levitating saint] AND [no God] there's a lot still left to wonder about regarding who made up the story at what point.
If so, they must be committing a 'disjunction fallacy', grading the second option as less likely than the first disregarding that it could be true in more ways!