Texted one person but my text was received by a whole group chat that I didn’t send it to

I texted a friend individually, but unbeknownst to me, the text was received by him and several other people we are in a group chat with. When I look on my phone my text is in my conversation with him. Everyone else in the chat, including him, sees this text in the group chat. Totally weirding me out that several people saw a text that I did not send to them.