Totally guessing but im sure its similar to people saying "Try coke once and you could die!". Technically true, if your coke is laced with Fent. Maybe get too high of a concentration in your air duster and you simply die?
Is it maybe an US-exclusive thing? Due to less stricter regulations maybe? I'm from Europe and no compressed air was 18+ or had warning signs like "causes instant death"
I'm in the US and haven't bought compressed air recently, but I definitely didn't need to present ID the last time I did.
This article says 38 states have age restrictions, but after a brief search, I couldn't find any evidence for this in my state (Utah). It's illegal to use it to get high and to sell it to someone with the understanding that they'll use it to get high. But now I'm curious, I'll have to ask the next time I'm at a store that sells it.
A DuPont study tried HFC-152a and HFC-134a on rats, dogs, and humans for time periods of up to three months with a followup examination 2 years with no adverse effects. LINK
I'm sure this has nothing to do with the USA'S proposed ban DFE last month despite it functioning as a zero-potential for ozone-depletions alternative to CFCs.
That red line you drew could just be explained by market availability of the new Aerosol that convienently excludes the CFC equivalents which existed before and were banned.