Probably sounds rather inane to say it, but does it truly matter? The BG series has a tendency to leave large gaps of "fill it yourselves" in its logic, one reason why there's so much content out there now I suppose. Heck, even that novel spin was an attempt at that; it's there, it's a thing. Same are the millions of fan fictions which could arguably be seen as the true story, only the original author of this whole franchise could reasonably claim otherwise.
Not an attempt to whittle this idea bubble into nothingness, mind you. Just not sure what it really adds beyond what already exists, doubly so for the mage PC - rats, who needs assassins or incompetent thugs when the rats will get you, hm?
Then again if they're anything like Bethesda's Dishonored's rats, then we have a problem.