It was an odd storytelling choice they made. The choice to bring in Don D for a crossover would likely never have been made if not for Don's past role on Y&R. I mean, that was the 'hook', right? Get people to tune in to see what happens when Brad's doppelganger is spotted in GC. In interviews with Don D, he seems dismissive of the idea that people will tune in to see Brad-related fireworks, but perhaps he was only playing down that aspect because he'd already filmed it and knew what was in the scenes (and what was NOT).
I figured as long as they were bringing him in briefly, they must have had some quasi-clever in-jokes to deliver even if they were not going to address Bill's resemblance to Brad directly. But from what I read, it was just Bill dropping in to rattle Sally and have some mild banter with Lauren. In the hands of a clever writer like Ron Carlivati this could have been a stunt to remember, but this was sort of flat...unless there is some other aspect of the visit that they have yet to reveal.