How is it wrong? First it makes some assumptions about the question and answers the typical version of the riddle. Then it answers the trivial version where there are no additional items. Seems like a complete and reasonable response to me.

Because if we weren’t then no class would ever learn anything, as the teaching would move at a glacial pace and cover material that isn’t relevant until you start on your PhD.

The link references “a/bc” not “a/b*c”. The first is ambiguous, the second is not.

Assumed by whom? Clearly not everyone.

How do you plan on that happening?