Many restaurants provide food and service before payment. At that point, it's a little late to refuse legal tender.

Restaurants that require payment before providing food have more flexibility.

I imagine if the restaurant staff called the police and claimed you were refusing to pay for your meal, and your defense was “but I offered them cash”, then that would actually be a pretty good defense. It’s hard to imagine the cops siding with the restaurant and arresting you for theft.

So I think you’re right, even though it sounds like a minor distinction.

No, it must be accepted for debts.

But a restaurant bill generally isn't going to be a 'debt' in that sense... if they only take credit cards and you don't have one after already eating your food, they're just going to write it off and ban you from the premises.

Or maybe, you just drop by and pay the next day -- like a decent human being :)