That's correct. But if you already have a debt to a business or human person they must accept currency as payment for that debt. I think you missed the whole point of my comment.
The long standing way food trucks work is you order, wait, receive food, then pay. Now, to get around this law, food trucks have switched to pay, order, wait, receive food.
Ah, ok, I'm tracking you now. I think the confusion is that is not been my experience. Every food truck I've went to go order, pay, wait, receive food.
I don't think your central premise holds, however. You may be reading too much between the lines or giving too much credence to a colloquial (and perhaps incorrect) interpretation.
"when a debt has been incurred by one party to another, and the parties have agreed that cash is to be the medium of exchange, then legal tender must be accepted if it is proffered in satisfaction of that debt. However, otherwise the selling party may set the medium of exchange to be anything they choose: dollars, bananas, precious gems, feathers, whiskey, etc. They may also choose to accept cash payment only via alternative forms (e.g., credit/debit card, check, money order) rather than currency itself."
The long standing way food trucks work is you order, wait, receive food, then pay. Now, to get around this law, food trucks have switched to pay, order, wait, receive food.