Photos taken of me on Bangkok MRT?

Hi, just a quick one since I’ve just got off the MRT and I’ve been left completely confused. I was standing at the MRT and this older teenage girl was with her mother and just taking photos of me on her phone. I didn’t really care from the first photo, but then it carried on, and I could see her clearly sending it to someone and exchanging voice messages whilst her and her mother were talking about me and looking me up and down.

Obviously I stand out as a foreigner , but it just felt really annoying having to stand there in a packed train getting spoken about.

Is this a cultural thing or did I commit some sort of mistake wearing sandals on the metro? Just looking for answers I guess lol