On my Department, (Northern NJ Municipal Dept,) we impound for many things that include, Suspended Drivers license. (Although we have released the vehicle at scene to a responsible party) expired or suspended registration. I have personally impounded vehicles when drivers were suspended for non payment of child support There are mulitple reasons to impound a vehicle. Did you ask why it was impounded?
Prior to towing, a usual inventory is taken (standard form on the tow sheet) Sometimes vehicles that are parked improperly and the plate is run, then its learned that the reg was suspended for non payment of parking tickets (scofflaw) then vehicle is held until payment or adjudication is made. Standard disclaimer, I’m not a lawyer nor have I played one on TV, yada yada…