He is probably right. A ganglion
, is an excessive collection , of proteinaceous material in the sheath, of a tendon.There is normally a small quantity of the same to help the tendon ( Part that attaches the muscle to the bone ) slide smoothly.This is not in anyway a dangerous condition, is is more common in those doing repetitive wrist movements, in the course of their occupation, like Typists & those that use the keyboards for long hours.
It can be left alone,or if it is big enough , to make you self-concious or is growing. it can be aspirated & injected with a steroid
or removed surgically.There is chance of recurrence with aspiration though.But do ensure it is, not any other condition.