A short circuit is a special case of fault current. If you left a wrench lying across two phases of a bus, that would be a short circuit. It's only one type of fault current (there are several).
If you connected the A phase supply to ground instead of to the A phase lug, then you’d have a bolted ground fault.
In either of these cases, the connection is solid. And it’s unlikely (but possible) that the breaker or fuse will open (clear the fault) in time to prevent an arc flash and/or arc blast. You don't want the breaker to be your only defense, so pay careful attention to how you make connections and where you put your tools.
The more common kinds of faults seem to just happen. For example, insulation rapidly deteriorates on a conductor and there’s a low impedance path to ground. As this situation unfolds, the fault current reaches a level that the breaker detects and the circuit opens. You won’t be able to reset that breaker until you repair the fault. The exception to this scenario is a poorly maintained (that is, typical) breaker might not open quickly enough or you might be able to force its sticky mechanism closed even with a fault.
