If you are even close to correct in stating that the "zap" was from an INCH away, then this MUST have been a static electric shock. That distance takes many many thousands of volts, and NO actual electrical supply to your system can provide that. Actually, the fact that you DID get a brief shock means it is VERY likely that the computer case WAS Grounded so that there is a place for the charge to go to. But that is not guaranteed. It is possible if you are "charged up" statically to discharge that to a completely isolated computer case which has no charge. "No charge" is still much less than a "charged up" you.
Even static electric discharges can damaged solid state devices when a current is forced THROUGH the device. Although the resulting current lasts only briefly, it can produce permanent damage. However, an incident that originates from outside the case is not likely to do that, because the discharge current flows to the grounded outer CASE, and not through any circuits contained inside it.