or are not aware of the names given to kids by celebrities.a) she was probably born on a different world.No fuck in their right mind no matter how stoned they are from the good drugs they save up for labour, is going to name their child "River Song"
b) you may not remember all the kids of hippies with names like Sunflower Moonbeam. eg Rainbow Sun Francks from Stargate Atlantis
or come to think of it, seen Firefly
now if River was a man then yes I would question the parents wisdom in calling him River, I would question a few other things about the Doctor as well, but also the parents.