Friend has small, visible hard bump on pinky-side of wrist for 2 days. Appeared suddenly w/o injury. Says it's tender w/ touch. Possibilities?

Many Choices. It could be an infection like a boil. It could be another infection. If it is not infectious consider inflammed blood vessels like vascultiis or erythem nodosum, it could be a nodular dermatitis from a variety of reasons. Your evaluation will include an examination to look for systemic reasons, possible needle aspiration or biopsy.
Ganglion cyst, no. Worries. It tends to come and go.