Struggling with parenting confidence

I feel like I second guess everything. Today really hit hard. We were at the playground and while I was gathering my things my 3yo hit another kid. His parent yelled “you don’t hit other kids!” at my son which was how it was brought to my attention. I ran over and asked “did he hit him?” And she said yes and then continued to yell “you don’t hit” at my son even though I was there. I picked up my son and tried to get him to apologize and he wouldn’t so I talked to the little boy and asked if he could do a redo with my son so he could practice gentle hands. And then we left after I rounded up my other 2 kids. Looking back, I wish I would I have said something to this other mom about how she spoke to my son. Like “I got it from here. He’s 3 and still learning, please be patient.” I am not a confrontational person, I am not a dramatic person, I’m not a “Karen.” I just want to do the right thing and move on. I didn’t say anything in the moment because my focus was getting my son to do the right thing and honestly I don’t do well in intense situations. But looking back I wish I would have stood up for my son. This is super hard for me as an self-proclaimed quiet and non-confrontational person. Any other quiet, non-confrontational people have any advice or encouragement for me? Please no unhelpful comments about how you would have gone into “mama bear” mode and chewed her out- that is not me and I want to model how to be respectful and also address the issue. And also I think that would have escalated the situation and that’s definitely not something children should witness. Thank you!