I think the difference is that they are holding your car. I don't know for a fact but I'd guess that cases where you HAVE to pay, they have to accept the official currency - but still probably limited to the "legal tender" definition, which is clearly different in Canada than in the video. I do know for a fact that a private business has the right to tell you to pay any way they want. If I say I only take grass clippings as payment for my services, no one can stop me - unless, again I *think*, my services are required (like a utility, healthcare, taxes, or impound etc).
EDIT: nmind, 7 laid it out above