What is this supposed to mean, “ well she’s not ugly” from exes girlfriend?

My ex told me he showed his girlfriend, ex now, a photo of me he took (he was a photographer) and he told her who I am and that I model. She said “well she’s not ugly” in response. I always wondered why girls do that especially in this context. Is this because I’m an ex or some sort of insecurity? Or what did she mean? He said the way she said it and her look was her not wanting to compliment me. So she forced something out to downplay my looks. I actually don’t even know what it meant. Him even telling me makes no sense.
What is this supposed to mean, “ well she’s not ugly” from exes girlfriend?
Post Opinion