How Can the Best Move be an Inaccuracy?

Yesterday I played my first classical game and I've analyzed it, but I don't understand how playing the first line here (bd3), was an inaccuracy according to the engine. 

Here it says nc7 would be clearly best. Only reason that comes to my mind is that the preview is done by some 1000 elo computer, which has no idea what's going on. I understand even for computer it's challenging to get it right in like 0.1 accuracy, but this is like evaluation done by a first time chess player.

I tried what the preview suggested was the only move, but it's quite absurd, because after nc7, pawn takes bishop (first line) and knight takes rook (first line) I've lost nearly all advantage. It's confusing to me how engine could not see couple moves ahead. 

About the game, I decided to be aggressive with white, as usual. I was somewhat outplayed and got off guard in the opening, but after the opponent missed quite clear idea in move 13 it was very comfortable to play. I was still a bit concerned about some sacking chances for black, but there wasn't really anything. I can post the game in the comments.

Chess Analysis Board and PGN Editor - Chess.com