Are Players Who's Not In My Party Can Affect My Quest?

I was doing reincarnation, struggling to kill the Bob
Suddenly 3 diamond armored players came in and they just smashed Bob so quickly
So very luckily, I got the corrupted treasure
Even one of them just threw out his corrupted treasure at the out of Bob's tomb
I think they can't see me and my chat but how is it possible

 

They were in the same world as you, and as for the last thing you said, they probably just ignored you.
And yes, other players can help with bosses.

 

1) They propably just ignored you
2) If you wouldn't get it you could return to Bob's arena
3) No, they can't affect your quest progress, but they can kill the same minibosses as you, which means you might have to kill them again

 

yes for example while i was doing ahc i was doing something (i dont wanna spoil that part of the quest) and another player interfered with the thing i was doing and they accidentally bugged the quest into making it so the quest book didnt update and it wouldnt let me finish the quest. sometimes they can help tho like with a boss or something