Am I overreacting? Sisters boyfriend come onto to me last night (I think)

Last night we had a family gathering for my Mother’s birthday and there was a lot of alcohol consumed. We were all having a great time. My sister and her boyfriend have been going through a rocky time but they’re getting married in April. I’ve know this guy since we were 8. So I went into the kitchen and he was in there. I was making a drink on the counter and he gone up behind me and put his arms around me and started trying to kiss my neck. I turned around and said WYF! Get off me. He said “oh no I thought you were your sister”. I just left the kitchen without saying another word and shortly after that got an uber home.

The thing is me and my sister looks nothing alike. I look like my dad and she looks like my mother. She’s got platinum blonde hair and mine is very dark brown. I have felt weird vibes on and off from him for years and as I said my sister and him are having a rocky patch at the moment but nothing too serious as they’re still getting married.

Am I over reacting? I’m 5ft dead on and she’s 5ft 7 too. I just don’t see how he thought I was her.

I really don’t know what to do. I don’t want my sister marrying a sleaze but what if he really did mistake me for my sister? It would ruin their relationship and my friendship with him is now gone completely imo