I have posted about this before but I just want explain why I think that it is so important the school actually uphold appropriate and consistent boundaries for all children.
I was being sexually abused by an adult male relative from about the age of 7yrs (my earliest memory that I can date). The abuse continued until I was nearly 14yrs.
At the age of 10 I was sexually assaulted by two boys who were in my class at school. It happened on at least 2 occasions with them both and on one further occasion with one of them. It happened at the house of one of them, the one I had known since we were both babies. At the time that it happened I did not think that they did to me was wrong, although I did think that if someone else had seen it then they would think that I was pretty disgusting. I had an incredibly confused idea about appropriate boundaries (who should see my body and who should touch it). My understanding of boundaries at that time seemed to boil down to thinking that it was shameful if people saw my underwear or something when I was playing and then at the same time completely believing that if anyone (or at least anyone male) wanted to see or touch my body then I shouldn't be bothered about that and that I should ignore any sense that this wasn't right. So I suppose I saw boundaries about my body as something for others to define and decide, therefore anyone who wanted to see my body - then that was for them to choose and for me to oblige and if anyone didn't want to see my body or underwear then it was my shame that I had somehow accidentally inflicted it on them.
What I really needed to understand, as a young child, was that boundaries were there to help me be safe and to keep me comfortable and that they were not actually there to stop people being disgusted by my body/underwear. I also needed to learn, through having boundaries demonstrated and upheld in places such as school etc, that my boundaries about who saw or touched my body, were not for other people (especially males) to decide.
When schools teach girls that they must allow a male child to see them get undressed because they need to be kind to that child, then they are teaching those girls a very dangerous lesson about the unimportance their boundaries. If they are also teaching children, for example the NSPCC PANTS rules and telling them that nobody should ask to see their privates, then the result will be very confused children who are unsure when the PANTS rules apply and when they don't. When children are confused then they are more at risk of being groomed. It is more likely that a predator will find a way to groom a young child who is either confused and unsure about her boundaries or who thinks that kindness is more important than her boundaries.
If there is a girl who is already being groomed or sexually abused in the class then she is probably relying on school to teach her how to understand, develop and assert her boundaries. In my opinion, where a child is being groomed by a manipulative and much more powerful adult predator then this is highly unlikely to achieved in a one off lesson about the PANTS rule, but it may eventually be achieved if other adults and and the school demonstrate what boundaries are for and that they should always be respected. The situation described by the OP most definitely fails in this regard and therefore it is failing all the girls and especially the most vulnerable girls. This is what makes it a safeguarding concern.