Did they get tapeout before or after the move? If before wouldn't they have to then do it again, possibly?
It could be they moved before the tapeout and that's why they were so cagey about commenting on foundry. Numbers I have seen thrown around for a finfet tapeout are $150m (without masks which are another huge expense) so redoing it on another process would be incredibly wasteful.
The problem is the company who owns GF also is a major shareholder in AMD and has people on the board. That is why AMD keeps getting bogged down in these awful supply agreements with GF.