You're assuming that baldness is A) purely genetic and B) that only one gene controls it. Both are incorrect.
Baldness can result from a lot of other things besides genes. Hair products, stress, scalp/follicle damage, and lack of care can all contribute to balding. I don't know your mother's family, though based on what you said, it's likely there's some genetic component to the baldness there.
Also, many of the genes controlling hair growth are spread throughout the genome. Diet and environment can play a huge role in turning on and off the genes that would cause baldness.
It's true that some common forms of baldness are on the X chromosome, in which case you'd be doomed for baldness -- presumably. There's the possibility that your mother never picked up that allele, or even that your mother (or even you!) experienced a mutation at those alleles to eliminate the baldness trait. And, as you noted, there could be something from your father's chromosomes that reduce or negate whatever protein expression (or lack thereof) that could be causing the baldness.