An ungrounded/unbonded metal counter will have static electricity buildup, and the metal fryer enclosure is bonded to ground. The static electricity wants to go towards the ground, so it uses your body as a conductor.

The shock from the fryer was stronger because it was bonded to ground by an equipment grounding conductor that is connected to grounding conductor of the electrical circuit, while the railing was (likely) bolted to the floor, resulting in a less optimal path to ground as it didn’t have a path back to the ground rods/grounding loop of the building’s electrical distribution system.