True as long as the engine is not running. Any changes to battery connections (including that tool generated short circuit) when the engine is running can create load dump whiich has been defined by ISO and SAE to be as much as 270 volts. Latest numbers have lowered that to (if I remember) something just under 100 volts.
Automotive electronics therefore also meet higher voltage requirements. For example, 5 volt regulators must withstand something like 60 volts without damage.
Never make electrical changes (not including a jump start) if an engine is running.
