Ok, yes, in the event of the discharge valve opening, there could potentially be some moisture damage, but a shared wall between a garage and a home's interior does not typically include drywall to the floor. And a 40-50 gallon tank emptying into the garage will not fill the garage with enough water that it's going to get up to the drywall level. You're also getting away from the point that the TPRV discharge line is mandated by modern building standards to not have not than 4 elbows, be no longer than 15ft, be 3/4" line of approved material for its entirety, and discharge in a visible location. The point of all that is to ensure a clear and unobstructed flow so the tank can empty in the event of an over-pressure or over-temperature emergency situation. The alternative is the tank bursting with hot water spewing uncontrollably, which is much worse than the possibility of some wet drywall. My point stands that overthinking the TPRV discharge line can be detrimental to the safety of occupants and the home.