How would you feel if your best friend called your boyfriend ugly behind your backWatch
But what does it actually matter what someone else thinks of another person's boyfriend? As long as the girlfriend finds him attractive, it really doesn't matter, unless the girlfriend is literally going out with him as a trophy :P Everyone has their own tastes and it seems your two friends have differing tastes.
I had a girlfriend a couple years ago who I really liked. I found her cute and attractive but my friends thought she was a little on the tubby side. I didn't fall out with my friends, we all have different tastes. They aren't the ones going out with her so it doesn't affect them how attractive/unattractive my girlfriend may have been in their perspective.
There's literally nothing but drama and upset to be gained by telling your friend that other friends are chatting about her boyfriend.
I thought it was entirely normal to comment on the attractiveness of a mate's girlfriend/boyfriend. Positive or negative. And my female friends do it too.
In my group, we usually say it to their face as well, and even then no one cares. I wouldn't worry about it.