Questionable puzzles

Sometimes the tactics practice drive me nuts. In most cases the solution offered is far superior to any other move. So you get in the mindset of finding that powerful move..

And then out of the blue you get a puzzle where two moves are almost equivalent and the solution is only better for a computer analyzing 9 moves deep. 

I am starting from scratch so I am still on the supposed easy part of the tactics, and I got this.

White plays e4 and black to play. Black can capture with the Bishop or Knight. If you assume that white will recapture with the pawn, then yes the solution Nxe4 is the best. But in fact White does not have to respond this way. She can play Kd1 or Na3. Yes the solution cxd4 is superior by a a small marging if you let stockfish run it for a bit. And the reason it is superior is because of several moves down the line (becomes a positional issue). So once you consider the possibility that White has other options this puzzle becomes almost impossible to solve. Perhaps I am mistaken?