You're mostly right but I assume what people are criticizing her on is how she said it. She's basically saying her sex life is "average" but by her explanation of average, she doesn't seem very enthusiastic. So she's kind of saying she's not really that satisfied.

It's just kind of a shitty thing to publicly say about the person you're in a relationship with. If someone asked you how your girlfriend is in bed, and you're in front of a big group of people who all know your girlfriend (or at least know who she is) and you answer with some really luke-warm "Ehhh... I mean it could be worse... she's alright I guess." that's just not something she's going to be very happy to hear about if it gets back to her. Same situation going on here.

edit: guess what I'm saying is that in relationships there's just some shit you don't say or make public, its like if your girlfriend asks you if she looks fat, it's just compliment fishing, she obviously wants you to assure her she looks fine, if you go "ya you look like a big fat piece of shit" (even if that's the case) well, hopefully you understand what I'm saying...