From my own experience and logic on the matter:
Astral projection and out of body experiences are two different subjects. I'd say your right on the imagination part. That being because astral projection is the extension of consciousness beyond your body or your physical awareness.
Whereas, the OBE is the actual means of journeying out with the spiritual or energy body.
Both of which can be achieved either intentionally or unintentionally. Both can be done with or without control. Or some combination of the two. The attempt of an astral projection could even lead into an actual out of body experience. But in the event of a successful experience - intentional or not - but with a lack of control, this just means you need to work on gaining control. If you happen to have times where you struggle expanding out, journeying out, or having extended periods of experience, you may be too grounded and need to work on not being so grounded.