What is an incorrectly specified font?

Screenshot from a recent Jeopardy game show broadcast

Eagle-eyed type nerds watching a recent broadcast of the Jeopardy game show will have fallen off their chairs at this font faux pas.

The correct response to this clue was “What is a font?” but note that the font used for the word ARIAL is in fact Helvetica. Oops. And it was such a clever idea to set the clues in the named fonts.