I believe he was indeed talking about the gnomish death ray.
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Gnomish Death Ray used to be able to Double Hit and Crit on both hits for upwards of 3-4k total, which at the time was a retarded amount of HP (lvl 60 w/greens had maybe 1.6k-2k hp?).
The period I level that warlock was between the time of the Death Coil Buff (which added the Horrify effect and reduced reuse to 2min) and the Gnomish Death Ray nerf (which lowered damage and eliminated the chance of a double hit).
Yes, pre-Death Coil buffs this would have been a different story. There were a lot of other problems with CC at that time which made Warlocks a free HK for any class in the early days of WoW.
Anyways....
I was thinking more about before death coil was even put into the game, then again my main wasn't a warlock at the time, so maybe i'm mistaken and that there was no such time?
Warlock Fear was OP at the start. Then Fear was nerfed repeatedly until Warlocks had no chance against melee, you just couldn't get any distance. Free HK to a rogue if caught alone. This was what inspired the Roguecraft videos by Mute (however biased, one sided and flat out wrong in some cases).
Then came patch 1.8, the Death Coil patch and this was when Soul Link came along as well if I am not mistaken. They were re-balancing the classes 1 at a time back then and 1.8 was the Warlock's time.
EDIT: Death Coil was always in the game I think, in 1.8 it got the 2s Horror effect.