I think you make a reasonable point, but this particular comment was wrong because the comment was rooted in the speaker's sexual preferences. It is unlikely that the speaker would ever describe a man as sexy because heterosexual men generally do not view other men through the lens of sexuality. Calling someone sexy carries a pretty clear implication that they're "a valid candidate for sex", an implication which men do not have to process while interacting with 95% of their co-workers.
I should hope that calling someone a "sexy married woman" would not intend to imply that she's a valid candidate for sex. Not that it's particularly tasteful either.
I take it you're suggesting that his acknowledgment of her marriage implies an obvious understanding that she is not available as a sexual candidate, but his reference to her as sexy still reveals his approval of her appearance with regard to her value as a sexual partner for anyone (in this case, her new husband, who he points out is lucky to have her)
