My mother's meatloaf is 'food grade' but i'll be damned if im going to eat it!
That is half way believable though, it is possible they might get their CO2 from a supplier that normally does beverages or something.
Jokes aside, I don't know any HPA system that isn't ran filtered, mostly because it would destroy the compressors if they aren't meticulously maintained (go talk to a SCUBA person... made that mistake once, they dont shut up about how filtered their air is lol). Point being, if you've ever rebuilt a HPA tank reg, you'll notice they have dirt and grime in them. From what I have been told throughout the years, CO2 is more traditionally a 'dirty gas' meaning it is not as pampered in the filtration process. Think tap water vs bottled water. Yes, the tap water in most cases is better for you than bottled, but then again- yuck tap water!