I submitted a ticket to support, but I would also like to report this bug in the forum to see if others have experienced the same thing. Also I would be curious to know if anyone has been awarded this achievement.
I joined a low population 1x local server specifically for the purpose of getting this achievement.
The achievement requirement is "Have at most 0 crop in all granaries as a top 50 player at the end of a game round.": http://prntscr.com/qi2ll1
As you can see, my best finish says I had 1 crop in the granaries. However I know for a fact, and can prove with screenshots that there was no crop in any granary.
My friend also got the same bug... his best finish is 3 crop. When he created a ticket to report the issue, he was told that he must have had troop starvation which gave extra crop.
Proof of top 50: http://prntscr.com/qi2lrp
Proof that crop balance was ZERO: http://prntscr.com/qi2le1
Proof that there was no negative crop balance, so starvation was not possible: http://prntscr.com/qi2l8k
My only conclusion is that the achievement is bugged, and that the servers are somehow reporting "ghost" crop that isn't shown in game.
More evidence of "ghost" crop can be seen if you NPC to upgrade a building when you have ZERO crop production. You can specifically enter the exact amount of crop needed for the upgrade in the NPC screen and perform the NPC. The crop shown after NPC will be what you specified, however once you upgrade the building there will still be 1-3 crop left in your granary.