I can confirm that this is infact right. I do have to say though I was rather dejected after getting through the entire instance (as well as killing the boss) only to find that we actually needed 4 players to finish the quest.
Was very surprised at the lack of any warning (upon entering the instance) indicating this to be honest.
did you not see the Heroic +4 on the mission
lol i know you can solo meany of them but still that is your warrning
+4 means 4 players recommended
+2 means 2 or more recommended