I dunno, I liked it. Every joke sounds bad when someone breaks it down like I did.

I got the mechanics of your response (the literal answer being funny because it's true while also agreeing on the "he's not") and even found it funny (let's say 56% funny).

But I considered it premised on being an (actual, regardless of if being done as a funny quip) correction of the grandparent at the same time.

Let's analyze this further, it's fun!