You said nothing inappropriate, Holdingoutforsummer. I can feel your distress about this, it is your child after all but I bet he is not the only one; the only one to get caught is more likely.
I do believe he will outgrow this. You are doing all the right things. By all means talk to the NSPCC who will no doubt reassure you. If you are going away on holiday, without any of his usual friends around, see how he behaves then. By the time he returns to school in September I am sure it will be a thing of the past.
There's no point in labelling him as Adhd, he is probably lively and more vocal than some other children but kids do vary.
My son (going on 46), had a phase of tickling other children, on their sides, when he was about six. His teacher told me and I was mortified. I can imagine how unpleasant it was for the other children. We talked to him about it and, like yours, he didn't know why. We tried to explain that nobody should touch other people' bodies, just as he shouldn't allow someone to touch his. He was a lively, vocal child. It passed, thankfully, and he turned into a laid back bloke. Hope he doesn't read this, can't imagine Mumsnet is his thing.
I won't begin to describe what I suggested to a little boy when I was quite small. I'd just learned something from an older child and wanted to impart my wisdom. We were at a family gathering and sitting under the table. About twenty five years later I had to sit opposite him at a wedding and remembered it, I hoped he didn't. I'm now 75 and blushing at the memory!
Kids.......
I am sure all will be well. Enjoy the summer holidays, your little boy will be more grown up when he returns to school in the autumn, school will become a bit more serious and he will have other things to think about.