They're saying "pit" not "pot" in that situation. The reason that they are doing that is because the fruit cookers allow a maximum of 4 farmers to cook fruit simultaneously. If you try to get any more than that, they will be confused and the player communication area will briefly display the message about the cooking pit. It does get a bit tricky when you have a lot of farmers who want to harvest and cook fruit. Each farmer will 'reserve' a spot at the cookers, even if they are quite some distance from the trees at the time they decide to harvest and cook fruit. We have verified that this is never a problem when you have only 4 assigned farmers, but when there are 'bunches' of farmers, it's really difficult to determine who might have 'reserved' a spot at the pit for themselves, since that all takes place behind the scenes in the code. You can assign as many farmers as you like, of course, but many of them will refuse until a spot at the fruit cookers opens up.