For static shock hits and the associated spark, the main component is the fast current transient as it enters the internal protection circuitry via external metal contacts or connectors. However, when you hit a ground plane that a product is sitting on or next to, that generates a huge electric field transient (because you've just charged up that plane with the static hit), and that electric field transient is what confuses the device circuitry as a result of the plane hits.
Good product design should prevent any corruptions of device operation from direct or nearby plane hits. That's part of the immunity testing (the EN 61000-4-x series) that you need to do to a product in order to earn the "CE Mark" that is required to sell your electronics product in the EU. And it's a good idea to do the immunity test series no matter where you sell your products, since it helps to ensure reliable product operation in the field.