One thing I often hear is that the quest is "not canon, except where it is." However, I can't find the original source of this. Some people on Reddit said the statement could be found in the quest overview before the quest is started, but I checked and didn't see any mention of canonicity.
The quest was intended as a joke and a homage to the Gower Brothers.
The fact that you can encounter the Black Knight Titan there without having done the quest is something that alludes too the lack of canonicity.
The quest literally goes "behind the scenes". Guthix is alive and just an actor. The 5 GWD1 bosses get along just fine. There are multiple Zaniks.
Heck, you have to describe yourself as some sort of bug just to get 'removed' and sent ot the Behind the Scenes Bar.
If there is an canonicty, it is likely a joke reference to a joke reference. Sort of like whenever Deadpool does his 4th Wall Breaks. It will be relevant in that context.
tl;dr .... don't take it seriously. Just take it for the absurdity that it is.