You don't know the context. Did he just hit someone or pull their hair? Did she hurt him? Perhaps he had been hitting all day and she needed to make a point. If she got down on his level before speaking to him - that is a good thing. Children do listen better when you are at the same height as them and have them look you in the eyes.
I would have mentioned the incident to whomever was giving the tour and you probably would have gotten an explanation.
VPK is a tough age since many of the children are in school for the first time here in FL. Is there discipline in VPK - thank God yes, otherwise, it would be a complete free for all! Did the school give you their discipline policy? You should get it in writing and have to sign it.
C.