Not sure why they decided to use that name, but in the wiki I have found the below, which strengthens the theory of it being related to the bone bearing the same name:
- The game's name Tibia is also a medical (Latin) name assigned to the shinbone.
- The Fibula is the bone placed behind the Tibia, and it is also known as the calf bone.
- Femor Hills is probably named after the Femur, the thigh bone.
- Mount Sternum refers to the Sternum, the breastbone.
- Villa Scapula is named after the Scapula, the shoulder blade.
- An island north of Fibula, called Calcanea, refers to the Calcaneus, the heel bone.
Again, the reason why they chose that name is not clear to me, but given the evidence above, it seems it clearly refers to the bone that has the same name, and it is not just a coincidence or a random name they picked. Maybe this hint helps unravel the decision of choosing that name.