Of course they are bluffing. They will continue to bail out Greece with more and more unfavorable terms until Greece becomes a Southern Province of Germany on the Mediterraean. That has been the plan all along and it is all Germany has every wanted since before the days of Alaric and Attila the Hun.
Germany should just start to buy up all of Greece. Let the Greeks move to Turkey, Turks to Syria, Syrians to “Palestine”.