The idea of "free beer" is if I'm giving away free beer at my establishment during an event, there are restrictions around that free beer. I'm not gonna fill up a tanker truck for you, I'm gonna kick you out if you start trying to resell it, I'm gonna cut you off it you've had too much, you can't get any if you're under age, etc, etc, etc.

It's free, but you can't do anything you want with it. Really it's free to drink on my terms - and that's certainly "free", but it's not "freedom" (as in free speech).

The recipe for soda is also open source - anybody can make their own carbonated soft drink. But I think if someone offered you "free soda" it would be pretty clear that they are offering you a specific soda whose recipe you almost certainly don't know, not the umbrella concept of "soda".