The fact that at 3 year old he insisted that he hadn't touched her leads me to think it may have been blown out of proportion, maybe he accidently brushed that area , who knows, I would be inclined to play it down now ,I always think a mom should go with her gut, and your feelings that this teacher may be touchy about your child would be enough for me , so why not check out other daycares in the area .Children of that age are often hyper, he may not have ADHD its best not to leap to a label when 3 year olds like to rush, race and play more .,mine were like that but in those days no labelling went on, now its the fashion .Good luck, use that energy he has in sports , games it is a fact that active children do well when they can use that energy positively get Dad involved with outside ball games .
I would request that he be moved to another class temporarily or permanently if possible. Maybe being away from the teacher and the children will sort them problem out. Kids can also pick someone to pick on and make up all sorts of stories.
If the same thing happens in the new class, then you know to take this further and have some therapy done on your son.
Maybe it is that teacher’s class or environment that is causing this behaviour.