Doesn't really look like it's been taken out for a graft, at least not anytime recently. My bet would be he acquired a atrophic nonunion fracture the same time he broke his tibia. The rounded edges of the bone look more like they've been subject to resorption instead of being excised.

Honestly not that rare for fibular fractures, though the segment missing is fairly large. So it's probably a fairly old injury.