There's a second way that it occurs. Mind you, this bug didnt exist until either changeset 18 or 19, so something in that changeset created this bug. It's only about a year and a half or two years old.

In any circumstance of reverse boom, (i.e. "your people demand a tax rebate" or "a drought occurs lowering your food production"), when the game does the math for those it takes your food or income production × 1/3. What displays after will often be .3333333 or .6666667 depending on the actual math. Clicking anything, like literally any button, will cause the math to correct and round in the proper direction.

It isnt just limited to the war room, but in the war room, standard turns can cause the non-rounded amount to show. Most typically tho, it is a bug that is a product of droughts and tax rebates, not necessarily a war room bug. I would bet the farm on the fact that he had a reverse food boom and was not necessarily in his war screen.