You know, I would have been miffed too, at being taken for a beginner when I felt that I'd really achieved something and made a noticeable improvement. That said, it was obviously not meant as an insult, and probably just fell out of her mouth as casual conversation. And definitely, if ishe is a beginner herself it's a natural thing to say because it's what she's all aglow about herself.
I'll add one: my favourite "insulting compliment" came from an middle-aged gentleman a few years ago who asked me and a (girl)friend of mine, as we arrived at a parking lot on skis out of the mountains with sleds and camping gear, if we'd "really been out there all alone" 
i.e. without any men
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett