I would go further to say that the Buzzworthy Bumblebee line is less a subline and more a packaging refresh / rerelease.
By way of comparison:
We have the 1990s "Classics" rereleases of G1 toys. Do we consider them distinct from the G1 line, or a variation of the G1 line?
Is the Transformers Universe repackaging of Energon Steamhammer a distinctly separate release to the Energon release or a case of packing variation?
Did the Unicron Battles, Powerlinx Battles and Primus Unleashed packaging refresh in Armada, Energon and Cybertron respectively represent a separate subline or a simply packaging refreshment? If it was a subline, what do you do with figures that were in both sets of packaging?
I think these questions can be helpful when trying to distinguish between which version of a toy you have, but trying to create a hard and fast rule for it is difficult.
I would personally say it was a packaging variation of an existing line, but wouldn't object to those who considered it its own thing as long as they weren't trying to push their own interpretation as the "correct" interpretation.