You're right and it could be harmless.
But complaining about being unsatisfied with your husband's penis in this situation is than likely not going to help her and her husband improve their marriage.
It could be like you have given examples of and be harmless.
I actually am unconcerned with the OP's possible curiosity or insecurity but more so with the lack of tact displayed by the wife in question.
"In this situation" = talking privately to her girlfriends.
"Lack of tact" = even though we don't know exactly what was said, what the context was, or what she was trying to convey.
The thing is, with a lot of sex or marriage problems, we simply don't know how to ask someone for advice, help or guidance. So we might just "blurt" the issue out amongst our friends just to see if anyone tosses back anything useful.
What I would imagine was really happening here was a wife who is dissatisfied with her sex life, in her mind it is due to her husband's lacking size (though we don't know exactly what was said or what else may be going on), and in this situation she may have thought her friends would have some suggestions on how to work with it and have good sex anyway. (I have actually seen a few threads by women on various forums in basically that same situation and she was simply asking for ideas or positions that would feel better for her).
OTOH, sure, if she was just being mean and spreading bad info about her husband and simply complaining out of the blue about his small penis, then wow, that is not a very good thing for a wife to do. But we don't know that. I don't see any reason to assume the worst of her though just based on the OP's post. Not enough information.
Look guys, I realize this topic is something you'd rather no woman ever uttered anything about, EVER. But the fact is that yes, sometimes we women do discuss things like how penis shape and size affect our sex lives. And yes, sometimes we will be completely honest even if that wouldn't flatter you. The reason is because we aren't talking to YOU about it, we are talking to our friends about it. Similarly, men don't talk to their wife/girlfriend the same way they talk in lockers rooms when sharing about issues and asking for guidance sometimes. And all you men know it would hurt our feelings if we overheard some of the things you say. But you don't intend for us to hear it, and for that reason, IMO, its really none of our business. Same goes for women in general, and the wife in the OP's post specifically.