Yes, but that QR code has no meaning or value until someone scans it with an officially approved app, which checks its validity. The simple fact that Apple allows it into the Health app doesn't give it any value. The airline will still scan the code and check it. They won't say: "oh, I see it's in the Health app, so it must be OK".
So why bother checking it instead of just allowing us to store it as it is, be it "standard" or not, in the app?
The purpose of the Health app is that users store their medical data in it. It's not its business to check whether said medical data is genuine or not. If I want to store bogus health data in my app, that's my business. I can enter an incorrect blood type, for instance, and Health will let me. So why can't I store an incorrect QR code, if that's what I want? What's it to Apple? If it's incorrect, then surely the authorities will not be able to scan it when I show it to them, but that's my problem, not Apple's.