The "close" operation is a lot like the "door close" button on an elevator that isn't connected to anything. It just gives occupants the illusion of control. If you "close" an active app, it does, indeed, kill it. But in fact all it does it move it to a suspended state. The fact that it disappears from your list of apps is a lot like the door close button. You don't see it anymore but it's still available. When you "swipe," however, iOS assumes you want to "re-activate" that app and use it. So it does so.
I suspect that the inconsistent behavior (between the multitasking bar and the swipe gesture) results from a failure to communicate among Apple engineers, especially since the swipe gesture was recently added to the mix. I see this a lot among engineers in the software firm for which I work. Each group thinks they're meeting the requirements for the functionality for which they're responsible but there isn't an arbiter to resolve conflicts between requirements.