Individual messages getting sent to groupchat

I’m in a groupchat with my sister & dad me & my dad have an iphone and my sister has an android if that gives more insight. I sent a message directly to my sisters number, a picture and one message, it said it sent to her as an SMS then my dad asked what I sent to the groupchat somehow the picture I sent directly to her sent to the groupchat? It showed the picture in the groupchat on his phone but not on mine or my sisters. Idk how this is possible but it sounds like a major privacy concern I’m not sure what to make out of it.