Arf... Eldar are kinda busted as beslubber at the moment not gonna lie. What was the rule he miss read by any chance, since I play eldar too. So I don't make the same mistake.
He had four farseers, and he thought that the eldrich storm strat repeated the whole damage for each psychic action, so instead of just once.
So, he read it that (assuming each farseer completed the psychic actions)
The first farseer did d3 mortal wounds to all units, the second would do d3+1, the third d3+2, and the fourth d3+3,
So he did 4d3+5 mortal wounds to my units, instead of d3+3. So in one eldrich storm he killed my librarian, one warsuit and four units of primaris marines.
Turns out, not the case lol. But that basically ended the game for me.