360mm is all one piece, if it can fit, than a 240mm can go in the same place leaving the remaining 120mm empty.
likely referring to the ability to mount a 120mm AIO in the rear and a 360mm elsewhere.
The only other scenario that you might run into is a case that supports a front mounted or top mounted 360mm radiator, but not necessarily at the same time as their full lengths might interfere at the top corner of the case.
Do you have a link to the case in question?