My son just started a day summer camp program last week. It's only for three hours a day, five days per week.?

Yesterday, he kept trying to yank my older son's pants down, as a joke I guess (he was laughing/thought it was funny). He had never done anything like that before, so after I explained to him that was inappropriate behavior, I asked him why he did it. He told me another child in his class at camp yanked his pants down last week. I heard nothing of this incident from the teacher. My son said the teacher immediately put the other child in timeout but did not say anything to him. The camp director assured me before I signed my son up that the staff don't ever try to "hide" things, i.e., incidences between kids. Am I overreacting here, or should this teacher have told me about this?? I know longer feel comfortable letting my son return to camp now. Please advise.