No idea. There are also lines indicating that the DU
is a Bhaalspawn in the traditional sense, not one somehow empowered directly by Bhaal somehow... but the Dark Urge is by default a dragonborn (IIRC you can even find default DU's corpse in game if you aren't playing as them) and that species didn't even come to Toril until the Spellplague, well after Bhaal was dead. And all the existing Bhaalspawn were dead when he came back in Murder in Baldur's Gate. Hence the significance of the whole Abdel/Viekang throwdown. So you have a Bhaalspawn sired by a dead god from a race that didn't exist yet, which would have died before the events of the game anyways.
Some real industrial-grade handwavium required to square the events of the game here.
