How is that an ad hominem?
I didn't see anything that could be interpreted as a personal attack. For this to be true, it should have read something like: "Only an idiot would consider this blog to be credible". Maybe post was edited, but as it stands by the time I read it, nothing of the kind was there.
Also, I agree that random blogs are not inherently more credible than simply stating opinion yourself. In this, I don't find Owain arguments on this subject credible.