Merchant still appears naturally even with "the doMobSpawning" gamerule on false

So everything's in the title, I'll leave a screenshot.

 

Context: I was making a Minecraft Map when I heard some Villager and Llama noises, then I found the Merchant even though I have disabled the doMobSpawning gamerule way before this happened.

 

It doesn't really bother me but I just find it weird that he appeared even if he wasn't supposed to