nonsequitur

Any abrupt and inexplicable transition or occurrence.

“Having a costumed superhero abduct the vicar was an utter non sequitur in the novel.”

Any invalid argument in which the conclusion cannot be logically deduced from the premises; a logical fallacy.

A statement that does not logically follow a statement that came before it.

(humor) A kind of pun that uses a change of word, subject, or meaning to make a joke of the listener’s expectation.