Re: Strong gass smell whenever I switch on the oven?

If by gas you mean the mostly methane natural gas with methyl mercaptan, that fitting was probably supposed to be black iron, not galvanized. Because the gas may contain some hydrogen sulfide that would react with zinc or copper. Also for reasons of physical durability.

Or maybe the wall was just unusually thin and it suffered some physical impact or something.

Agreed. I didn’t know why but knew it should have been black iron, plus the correct tape or sealent.