The inspect functions throwing an exception when handed a method wrapping a non-function callable instead of returning False is a definite bug.

The behaviour of MethodType when handed a non-function callable is cryptic, but not actually a bug: the problem is that it expects to be able to delegate accesses to __name__ and __code__ to the underlying callable.

A docs bug to clarify exactly which accesses are going to get delegated would make sense (and perhaps make MethodType.__dir__ a bit smarter about that delegation), but it's a separate issue from the one Jeroen has reported here.