The picture is most consistent with a plantar wart.
A common presentation in clinical practice as well as the boards is heel pain or the parent suspects the child stepped on glass or another foreign body.
Depending on the size, it can also present as severe heel pain.
In the question they might divert you into suspecting it is an injury by noting it was detected after playing basketball or another sport.
The Differential would of course include
- Calcaneal Osteomyelitis
- Cellulitis / Abscess
- Foreign Body
Pay attention to what is being described and don’t be diverted by the red herrings