The divide isn't clear because one person may consider themselves in a poly relationship and another person may view that relationship as swinging.
People have a tendency to assign their own values to the definitions and then look at how other people manifest that definition through their own lens of values.
We've seen that in these forums when some people think that only a commitment over a long time would qualify as a loving relationship where others view the nature of the connection rather than the quantity of time. Both manifestations can exist under the same definition.
For me, it makes more sense to not assign personal values to definitions because they usually try to make such definitions mean more than they actually mean, and the usual purpose of doing so is to exclude certain identities for the sake of conformity.