Hi Robbie.
" Mr Alekssev was playing from, you got it, memory!"
A little bit of home prep that was all.
The game you posted was played in 2013. But in 1999 in the same position as Black:
H. Akopyan - I Krush San Francisco 1999
Irena took the same 'naive pawn' 5...Nxe4 and won!
If Alekseev did reveal in the post game analysis it was a prep'd line
It would have been to get her into a certain position and he would take over.
players graded 2700+ are not too bad at playing such positions.
All he required was this very difficult Black position to handle and her ticking clock.
His box may have even told him he was OK. That was all he he needed.
(What were the times taken - according to you Alekseev used what...5 minutes?)
If as you suggest he memorised all his computer analysis she too would
have to play exact computer moves.
I've not even looked but I know that will not be the case.
So if we take a wee look at this line where Irana naively took the pawn
and perhaps inspired by the forgotten game, Bakian - Degraeve, Belguim 1997.
Maybe there is fertile fishing grounds with sacs on e6/f7 knocking about.
1.e4 c5 2.Nf3 d6 3.Bb5+ Nd7 4.d4 Ngf6 5.0-0 Nxe4 6.Re1 Nef6 7.dxc5 dxc5 {The most common choice is/was 8.Bg5 } 8.Bc4 e6 9.Ng5 Be7 10.Bxe6 0-0 11.Qe2 Nb6 12.Bxc8 Nxc8 13.Nc3 h6 14.Nge4 Nxe4 15.Qxe4 Nd6 {OOPS! Black played this and resigned, he was possibly thinking after Qxe7 he had Re8. So the game was lost to a blunder and the idea lay buried.}
When good players are noting up their losses read the white stuff as
well as the black. (look in between the lines.)