I don't find it offensive personally, as I don't fit into either the skinny or curvy category, but I don't think it does any good in general. For a start, it's not as black and white as skinny vs curvy - I'm not skinny, at size 10/12 and being 5'9, but I'm not curvy either...and I would imagine there's a lot of other 'in between' girls too.
And putting down someone else's body shape in a bid to big up your own is pathetic, petty, makes you look jealous...and she makes it seem like girls are just pillows for men, like we need big bums to be appealing to men or something, or like our sole purpose it to be 'held onto at night'. I think it's problematic but then again there are a lot of songs that would be problematic if you were to dissect them, this one has just caused outcry because it's a woman saying it and the feminazis have gone into overdrive..