You can make a case for it
The argument basically goes that the forfeit is a one-time thing: you forfeit any extra attacks you had at the time. Great Cleave grants extra attacks after this point: when you forfeited them, you didn’t have them to lose, and now that you have them, the forfeiture is already a done thing.
Considering how absolutely atrocious the Whirlwind Attack and Great Cleave feats are, and how non-trivial a bag of rats actually is (to say nothing of setting up such a situation without something as abusive as a bag of rats), this isn’t really that unreasonable from my perspective, but YMMV on whether or not you buy it’s what the authors meant.
It doesn’t ultimately matter, because plenty of definitely-real options exist
In the context where this was raised, it doesn’t really matter whether or not you buy that particular combo: plenty of other combos are more unambiguously functional in similar situations. I take the other answer at its word that this particular combo was the origin of the term, which justifies highlighting it even if it arguably doesn’t work.