Seems like you’ve got it tbh. Fragment implies a floating piece of bone, I don’t think they’ve made a typo. If any doubt you should have the secretary’s number and call ask them to get someone to talk you through it.
EDIT: You can get an avulsion fracture (bit pulled off) of the calcaneum which would leave a fragment floating about. Does that make sense/make it any clearer?
Out of interest did you injure it by landing on the foot from a height?