My boys both had bare bellies their first 6 years. Only in the last couple of years have they grown more hair and I have had more grooming work to do on them. They are getting hairier with age.
Seriously, their bellies, inner legs, and ear canals . . . lots more hair to contend with.
It's also possible that the breeder had already started to do some grooming on your baby's belly. Wait a few weeks and see.