I think I messed up messaging her. Why are girls so cautious about guys even though its just an online chat?

I wasn't getting replies from the other girls on Instagram like Aishu so yesterday I followed some girls on Instagram whom I knew in my school days and even messaged one of them. The first 5 letters of my name and that girl's name whom I messaged are the same. I kinda remember her in high school especially when she used to get some trophies or medals for something and teachers used to call her name and some of the boys in my class used to tease me as we had similar sounding names. I guess she was a year or 2 my junior so she is 20 or 21 now and I turned 22 just 4 weeks ago. But after I messaged she is trying to recall whether we ever met personally in school or anywhere or not. We were in the same school and have similar sounding names but still she seems a bit cautious and idk why even though its just an online chat. She definitely isn't happy that I messaged her. She keeps asking whether we met before or not. We actually never interacted in school. I just know her when teachers used to call her name for some prize or medals in school. I guess I messed up messaging her