But how???

Only 18 centipawn loss for white??? It's ultrabullet!

This could be due to the fact that white is a GM.

@A_0123456 I'm assuming you are wondering why 18 centipawn.

White played enough "correct" moves to compensate for the loss of 2 points (per the engine) on move 3. I didn't do the calculation to see if 18 is correct. Let's see. There is a 0.7 drop at move 2 and the missed mate in 9 at move 21 probably does not count because the score is 29.1 which is greater than the cutoff of 10 (so I've been told). 2.7/26 ~= 0.104 = 10.4 centipawn.
Not knowing how deep the engine was set, at least this answer is in the ballpark.

It's not 18 centipawn loss. It's 18 average centipawn loss. It's easily possible by a combination of skill and luck (I leave the question of what the balance of those two is in this particular case to that select few who find it interesting).

The game is only 26 movesand black made lot of mistakes, that can be immediately seen by white