That doesn’t prove it’s a bug, that just proves that blues often have no clue what the hell is or isn’t meant to be in the game.
Having a tooltip stating you need to go to a sanctuary to phase and wowhead article stating that this was intentional leads me to believe blizzard intended this 100%.
So after looking into this a bit, turns out that no. It’s not a bug. It’s intended:
Whether this is a temporary change remains to be seen. All I know is it’s a really stupid move. Time again I keep thinking they can’t possibly make a more stupid decision. Time and again blizz proves me wrong. SMH.
It was intended but as of a new hotfix either live now or in future it will be removed. The idea was if you grouped up with a friend randomly in Bastion (and you are party leader), your friend would have to go to a Shadowlands Sanctuary location (ie Oribos or a zone sanctuary like Heros Rest in Bastion). Once that condition was met then you can do content together. The idea for the new system (as Blizz themselves confirmed it was intended) was to prevent realm hopping.