I assume said 4 people were either level 80's or were at least at 1/4 of their max health if twinks or 1/2 if non-twinked.
If you have proof of said feat I'd love to see it, but at this moment in time based off of personal experience, I highly doubt the claim.
I just logged on my shammy, and although not properly reforged for elemental, is in full MoP gear. 4x 85 dummies in Org, two chain lightning casts.with alch trinket and jade spirit up for at least one of the casts, 15 total hits, for whatever reason 1 bounce didn't happen... 500598 damage total. Highest crit at 60.2k.
500k damage, take into account his better gear and Tarcegosa proc, I'm gonna give it another 50%, so 750k damage on 4 target tops.
Then we get to bring that back down again by at least 40% because of base resilience, so around 450k damage.
4 players = at bare minimum 150k each = 600k, 150k short.
4 twinks = at bare minimum 175k each = 700k. 250k short.
So when I give advice on a class, it's because I have one and have played one. It's not because I've seen someone else magically dispatch 4 enemies at the same time.