Questions: Health & Fitness

So I've been going to this same gym for 3 years and attend various yoga classes and have never had any issues with anyone saying my attire was inappropriate until yesterday. I had a call from the yoga instructor that a lady complained and had sent her this picture saying it was inappropriate. It was an intermediate vinyasa yoga class that my girlfriend and I take together, I think there were a total of 12 students in the class including my girlfriend and I. I have worn yoga pants to these classes for years, and everyone else in the class was too. So is this BS that I'm being singled out as a guy, my girlfriend is pretty pissed about it and thinks it was an older lady that was behind me but neither of us really remember for sure. I've had this same instructor for various classes and she's great. She said she doesn't see a problem, but just wanted to let me know. She said she thought it was inappropriate the lady took a picture of me during class and said she discussed that with her already.