I disagree. It is more than a stretch to call a medical exam sexual assault.
Regardless of whether the nurse's actions were misguided or a result of misinformation, one could reasonably (and successfully) argue that her actions still fall well within the boundaries of a normal medical exam and she was doing her due diligence by examining the boy for what she thought could be a medical problem.
I guess I'm mystified by the retraction obsession in the U.S. I've lived all over the world with my children and never encountered the belief that a one-time incident of retraction with cause horrible permanent damage and the person who did it is evil and deserves to be destroyed professionally and financially.
So yes, it can be sexual assault and this boy was old enough to understand what was happening and to have consented or not...besides, his mother who had medical proxy, did not consent...it is sexual assault and should be treated as such.