Can a ganglionic cyst be caused by someone grabbing and squeezing your wrist pretty hard?

No.: Repetitive motion causes ganglion cysts, like typing, using a hammer, or driving all day every day. I even saw an anesthesiologist get one from incubating people all day. Treatment is aspiration or surgery.

Possibly: A ganglion cyst is usually caused by trauma to the joint capsule. The capsule is a cushion between adjacent bones. Overuse or straining are typical traumas. Grabbing and squeezing depending on the magnitude of force are possible sources of trauma.