the bumps are scars from fighting.
Actually, all male giraffes develop calcium deposits on their skull with age that give it the bumpy appearance, even if they are kept from fighting. Eventually the deposits build up and form three large bulges on the head that make them look almost like they have five ossicones. Some females also get them, though never to the same extent as the males. Giraffes are truly bizarre creatures with some fascinating anatomical quirks. It's awesome that you've gotten to work with one.