An entire episode was written for Robin Williams.
The show’s writers wanted Robin Williams to appear in 1991’s fifth season of The Next Generation. The actor was a fan of the series. He even made a reference to it in Mork & Mindy. On the other hand, the show’s writers were fans of Williams, and that’s how the idea of having him as a special guest came up.
The writers created a character just for him, but unfortunately, although Williams wanted to be there, he couldn’t due to problems with his schedule, as he was filming the movie Hook.
Of course, this hand gesture means "read between the lines"...
He came up with it for the character. He's the reason it's in the show. That's all that anyone needs to know. Pointy ears weren't a new thing, either.