He isn't being shady though. I think Bill favorites a lot of delusional tweets like that because he honestly finds them funny and can't imagine anyone being so serious.
I'm pretty sure Bill didn't favorite the tweet because of the shade factor. He favorited it because of the Britney part. I'm pretty sure he said he loves Britney.
The link redirects Bill to his calm and collected response to GaGa. He liked that tweet because he took it as "praise" and was ecstatic that someone else wanted there to be communication between GaGa and Billboard.