My 4 year old hit someone today

My heart is just broken. My 4 yo son has always been a handful. He’s triggered by everything, screams at us and his teachers. He’s been observed by a behavior specialist and then said he needs OT so we’re waiting for that to start. He’s never been physically aggressive except for a push here and there (and of course he had a consequence). Today at an indoor playground he pushed another little boy and hit him several times in the face. It was awful. I was mortified and felt so helpless. He was in tears because everyone was yelling at him. I didn’t even have him apologize because he was such a mess. I apologized to the family and left (with my other 2 children crying and screaming). I did the follow up of what to do instead and how that’s unacceptable. He did say he felt bad. I just feel so shattered. I never thought he’d capable of something like that. I can’t stop thinking about it. I know I need to forgive him but it’s so hard. I feel like I’ve failed because my kids are just so rude and mean. I have NO idea where the my get it. My husband and I are very mild mannered.