I assume you both think the paper's methodology is unimpeachable, since otherwise one of you would have said something about that instead of just making ad hominem attacks.
How is this ad hominem? This is like an article about cardiac health that says that we need to immediately stop administering Aspirin to the entire population written by an OBGYN with a plumber that sells Tylenol as a co-author.
It's an ad hominem because you're saying bad things about the author rather than bad things about the paper. There's a reason that blind reviews for journals exist.