The intent of the comment was probably not ad hominem, as if it were rephrased like "trusting ddg is silly" because then silly is modifying the act of trusting. But as-written, silly is modifying anyone (a person) without distinguishing whether silliness is the cause or the effect; if silliness is the cause of the trust then it's an ad hominem attack. It would be more clear-cut if instead of "silly" they said "low intelligence."