Personal message sent to android sends to group chat

This happened while using an iPhone 16 Pro Max with IOS 18.5. I realize there is a newer update available now (18.6.1), but this is still worth mentioning because it is a huge breach of privacy.

I recently sent a text message to my mother on her Android. I later noticed that my family group chat was replying to the message, even though the message didn’t appear in the group chat, only to my mother directly. For the past few weeks she has been replying to our personal messages in our group chat, and I just thought it was her old android causing the problem, but turns out my messages were really sending to the group chat without actually appearing on my end.

Has this happened to anyone else? I deleted both chats and started fresh and it seemed to fix the problem, but what’s stopping it from happening in the future.