No, this is not to be expected from an eight-year-old. Set firm limits with her about this. In the process, have a conversation with her about the possibility of similar behavior in the past. There may well not be any history in this regard, but it is important to ask about it.
Honestly,I'm no doctor.but an eight year old is old enough to know she should not be touching his private.also he is only 2 years old,you do not want him to grow up thinking its ok they just want to explore.you know what i mean? I would just have a talk with both of them.cause to me HE KNEW IT WAS STRANGE AND HE WAS UNCOMFORTABLE BECAUSE HE WOULD HAVE NEVER TOLD YOU .NOT PUTTING YOU DOWN AT ALL.I HOPE THIS HELPS LOVE :)