@•Ace•:
It seems Caribou can get full even though he has infinite space. When Caribou stores things inside him, it satisfies his stomach. The cover page shows Caribou feeling "full", but once the feeling goes away, he can continue to store more things inside him. The objects he stores don't get digested at all. Because Caribou can get full, it limits how much he can store at once even though he has infinite space. In conclusion, Oda found a way to make the ability less overpowered.
@King:
It's just a visual gag showing that he succeeded at "eating" the factory.
Oda already nerfed Caribou's fruit at the end of Fishman Island, when he had to get rid of the mermaids in his "belly" in order to store the palace's treasure.
Maybe that was just an excuse to not drag the arc any further with a "we have to save the kidnapped mermaids!" mission. But it happened anyway.