There are various types (or degrees or flavors or something) of libertarianism. Minarchy [0] is one type, but doesn't seem to be the most vocal from what I've seen. There's even libertarian socialism [1]. The most vocal type seems to be anarcho capitalism [2] which is pretty much the no government whatsover group.
[0] https://en.wikipedia.org/wiki/Night-watchman_state
As will adherents to every political persuasion. Some even go so far as to violently purge their impure members.
You may not think they are credible, or libertarians, but I'll ask you not to deny my lived experience just to support your personal idea of what a libertarian is or should be.
The libertarian argument that you're almost certainly mischaracterizing there is about the pandora's box that is opened by allowing the government to decide what is or is not "poison" (which is of course an absurdly emotionally charged word picked by their opponents). Consider that some governments want to restrict sugary food on health grounds. Sugar isn't a poison but once you accept the principle that governments can ban companies from selling "poisoned" food, the definition of poison immediately comes under attack and sooner or later means almost nothing like what you'd expect.
There are always going to be grey areas, such as the line between "safe" and "unsafe", and Libertarianism doesn't provide any guidance on where that line should be. The government's role is to define that line, and the courts to interpret it as part of checks and balances.
Were they libertarians? Well, I can't say for certain, but I think that seriously trying to argue they weren't gets well into No True Scotsman territory.
Regardless, almost every self-proclaimed libertarian I have ever come across has absolutely argued against government regulations, with the possible exception of those supporting property rights.