The Mysterious Manor?

I just went to an island at random and came across a big building with a big gate with a bunch of NPCs attacking it. Then an NPC (???) says
“The pirates! They’ve returned! They’ll tear this place apart within seconds. You there, traveler! You must stop them! Believe me, it won’t be to your disadvantage.”

then it says The Mysterious Manor in all orange and says to keep the pirates away from the gate for two minutes. I succeed and he says

“ That must’ve been the last of them. You cannot believe how thankful I am. Please, meet me in the courtyard.”
The Mysterious Manor SUCCESS
But when I meet the guy in the courtyard
I can’t talk to him and his name is Old Man.
I’m only level 33
What is this?

 

It's a world event, a hidden secret to kind of help make the world feel more alive. When you defeat the pirates he gives you access to a farm, if I remember correctly.

 

Indeed he does.

Adding onto what btdmaster said, these world events occur only once per class.