Depends on where the 12v was drawn from. If it was connected to the 12V cigarette lighter port (that thing has a 15A or 30A fuse in my car) that should be expected load, but maybe not 2+kW drawn constantly for hours directly from the battery's leads.

Anyway the Tesla doesn't generate power during driving like a regular car does, so the 12V power is always topped up from the main Lithium battery and the DC-DC converter needs to be reasonably sized to accommodate eg. 600W supply. If power was taken from the regular port than i would count it as regular use (eg. when camping i would count on my car to charge things, even if it uses fuel and generates 0 km/miles.)