Sounds to me like the idea of a training facility beside the new stadium is unlikely to happen, hence the pivot to plan B at Riverside. I do wonder how much they'd be willing to lop off of the Camperdown complex, though I'd assume the stadium and the crematorium are non-negotiable.
Considering the willingness the SFA and UK Gov't have to provide funding for Riverside and it being further ahead than Nou Campy, the relative ease of developing that land for a training facility is more than worth favouring that option over spending far more time and money to get adequate training facilities at Camperdown as well.
As for Gardyne, I never thought it was planned on being a permanent location, though I'm not surprised that given its popularity it is being taken into account for the Nou Campy office plans.