It's not a rebuttal - he's not trying to say Scott is wrong. He's pointing out Scott is a hypocrite. An insult is not an instance of the ad hominem fallacy.
>He's pointing out Scott is a hypocrite.
Gruber, not Scott. He's not talking about the original writer, but for the guy that quoted him.
He is arguing against Johns stance on AMP by calling him a hypocrite citing his views on iOS, literally a perfect example of an ad hominem.
> "the cat is out of the bag".
This is where he says his argument is rubbish because he supports iOS.