Anybody can give their 2-weeks notice at any time, and a forcible relocation obviously increases the risk. A competent manager knows how to ask their employee what their plan is while giving them enough wiggle room to leave lines to be read between, and also would have been considering possible contingency plans even if the employee said "I 100% without a doubt would love to move to this new location and RTO".

I think the chance they are sinking their buddies is unlikely. It sounds like this is already some time in the rearview and it's not like they exposed any direct info by saying "I've heard from other engineers"