Did they diagnose him with any ligament damage? They were probably trying to figure out which ligaments were damaged, and if his foot was moving in certain ways that it shouldn't be, or hurting in certain ways, it indicates that certain ligaments are damaged.
Certain ligaments are usually damaged when a foot turns in, and others are usually damaged when a foot turns out.
This is all very general info, though, and you should ask the doctor for specifics on why he asked about your son's foot.
Hello, I really don't know, I would ask the podiatrist, he/she should surely know why.