@Sophie-Louise0 , You can be sure that the advice above from @Mike-And-Jane0 is correct. There's really not a reasonable reading of the dispute moderation policy for reviews that would deem the review from L*** to be in any kind of violation, regardless of your suspicion that the guest was responsible for the gas smell. In fact, the guest's primary complaint was not about the gas itself, but rather the fact that nobody answered his calls for help. The relevancy of that is beyond dispute, but guests can decide for themselves whether they feel a host needs to be on-call at all hours whenever something goes awry.
I'm afraid you're getting a baptism by fire here; not only about the futility of disputing reviews, but also the fact that if you draw a safety or health hazard to Airbnb's attention, your listing may get suspended regardless of whether the guest is at fault.
But if it's any consolation, your public response to the review was very classy and professional, and should assuage any concerns. Rather than resorting to unnecessary censorship, have a little faith in your prospective guests' intelligence.