Nice fun question.
I imagine some people will get the right answer for the wrong reason, but at least they will not b emoaning about "I want my point". More people will get it right for the right reason. So perhaps the proportion of wrong answers will be rather smaller than usual.
One potential gripe though: the reference given in the explanation doesn't explain what IsNumeric returns for NULL - but no-one should complain about that, as it probably isn't documented in BoL.
I've always found it a bit disappointing that IsNumeric(Null) doesn't return NULL; after all, a NULL value doesn't contain any non-numeric characters, so it's not not numeric; and it doesn't contan any characters that are numeric, so it's not numeric either; so it should surely return NULL; just yet another case where (T-)SQL gets it wrong with NULL. But then IsNumeric is such an awful function anyway that that's teh least of its worries (perhaps the biggest is its name).