According to the logs linked in the video, there was barely any self-healing involved indeed. The Bard and the Ninja used one Second Wind each, Ninja tryharded a bit with Bloodbath... but otherwise the 'best' self-healer was the Warrior with a whopping 60k through Storm's Path. Poor thing, his single Equilibrium use was a 100% overheal!
But yes, the biggest contributor to let them get away with so little healing overall was the great cooldown mapping; pretty much every major raid buster had Addle, Reprisal, Shake it Off, Divine Veil or healer shields running.
Also, holy hell, nearly 80% Balance uptime.