It certainly is enforcing a Christian rule on non-Christians. "Christian rule" here means not "rule found in the Bible" or "rule adhered to by at least 40% of Christians" or anything like that but "rule wanted only by Christians, for specifically Christianity-related reasons".
The only plausible reason to forbid buying alcohol on Good Friday in particular is that among Christians Good Friday is a solemn holy day on which drunkenness would be exceptionally inappropriate.
(Other hypothetical things that I think would be "Christian rules" in the relevant sense, just to make sure my point is clear: A rule forbidding anyone to speak ill of any canonized Christian saint. A rule forbidding commercial transactions on Sundays. A rule obliging everyone to attend at least one service in an Anglican church every Sunday. None of these is regarded as obligatory by most Christians. Any of them, if made into law, would be an obvious example of Christians imposing Christianity-specific obligations on others. That the obligations aren't readily derivable consequences of Christianity as such makes this worse if anything, not better.)
I agree with you on all the facts here, but I still don't think talking about this as Christians enforcing a Christian rule on non-Christians is a good way to think about it.
At least parts of Italy have a law against stores being open on Easter Sunday, although they are allowed to be open on other Sundays. You could say that they are enforcing a rule which simply has Christian motivations on non-Christians, and you would be right in a certain way, but I think wrong in a more important way. The real reason for the law is to make sure that employees can be a...
Another month, another rationality quotes thread. The rules are: