OK, so for a start, it's one thing for multiple people to disagree with you and another for them to be dogpiling. Given that the original poster is not hostile to the headline, I'd say the reaction is... fairly genuine? I can definitely tell you I'm not particularly emotional about it... you're just wrong on the technicalities of the headline, so people telling you that isn't that surprising. I'd argue the framing of the headline is actively seeking that outcome, it's arguably ragebaiting.
Also, I get that you don't understand why the headline is problematic, but I'm telling you that's you not understanding how to make a good headline. I'm trying to explain how framing shapes the message, particularly with a headline and particularly online. This isn't some esoteric thing, it's something journalists actually study and train about. This headline is meant to cause a reaction and frame the issue a certain way by providing a misleading comparison. That's bad form.
The conclusion of the paper being reported on is neutral: inhalers emit some amount of pollutants, most of those emisions are caused by a specific type of inhaler, there's some incentive to find a less pollutant alternative. All good so far, as often with these problems the study itself is fine.
The headline takes that neutral takeaway and frames it a certain way. I actually would believe that the journalist that messed it up did so because they thought "cars are understandable to most Americans" and didn't think it through. Mistakes happen. Being less charitable, but likely more realistic, the journalist probably thought framing it in terms of "your asthma is as bad for the environment as road traffic" was a deliberate way of increasing impact by providing an out-of-context statistic to generate more traffic. Either way, if I were an editor here I would have asked for a revision to avoid causing that bit of friction and misinformation.
It's okay to not get that because... well, the flipside of that being a bit of a technicality is that it's fine to not be cued in enough to know. But it's weird to double down on how the undesirable outcome they are causing (people are mad at the framing) is what justifies the mistake in the first place. After a few goes around the loop that just comes across as willfully ignorant.
Also, it's weird that you are asking how they should have phrased it when my first post already provided alternatives. You keep coming across as not having read the stuff you're responding to, which doesn't help with the whole "willfully ignorant" thing.