If your towing state to state (interstate) you can tow double/triple trailers portal to portal regardless of local state laws.
Now, if the friend that leaves his driveway to go a couple towns over within the state (local tow) for some recreation activity, then yes he is in violation of that state's law.
*Current: 2005 Ford F350 Crew Cab Dually 6.0 diesel 4x4*
*Retired: 1987 F350 Crew Cab Dually 6.9 turbo diesel
2007 Forest River WildCat 32QBBS