Um, no. An ad hominem argument would be if I were attacking 551199's character which I'm not. Instead, 551199 cited D'Souza as a reliable source and I attacked D'Souza's character. See the difference? Good.
I am however, impeaching D'Souza's credibility as a source.
..based on political views you find odious, rather than directly attacking what you think is right or wrong about the particular (unrelated) statement in question. That is an ad hominem argument.
Well, I didn't know that a felony conviction or cheating on your wife were political views. However, given the current President, perhaps you're right.
Specifically, pointing out the obviously biased nature of a source calls to question the credibility of said source, even before we get to addressing the argument itself.
Again, the arguer was+is 551199 and I'm not attacking him. However, he did trot out the odious Dinesh D'Souza and I felt it necessary to put that cretin into his proper context. So I'm not attacking the arguer; I'm attacking his alternate facts.
I am however, impeaching D'Souza's credibility as a source.