What did I do wrong?

Hey im a rather new Player and level my second character (im in the dragon isles). When I quested through the azure span I flew a bit around and noticed like 3 players killing Mobs in a place called brackenhide hollow. I was just level 63 but joined them in killing Mobs there just for fun but realised it gave me good xp so I stayed a bit. I just waited for the other higher level players pull and then helped to kill them. Also the mobs names weren't gray so I got xp and loot. There were like 4 players standing on a roof in the area but not helping and when I got bored and wanted to leave the area I noticed that 3 of the guys standing on the roof messaged me to basically f off and were pretty salty.

I just wanted to know what I've done wrong to avoid it in the future :)

(Sorry if it's obvious and I'm just dumb)