The equilibrium condition in which two actions have equal expected value against an optimal opponent, which is what licenses a mixed strategy. The better chooses a bluff frequency b=s/(1+2s) so the caller's bluff-catcher is exactly EV=0; equivalently the caller continues at MDF=1-α. At the table, indifference is a licence: pick whichever mixed branch performs better against your actual opponent at zero theoretical cost. It is not a claim that you do not care — it is the statement that the opponent has been made not to care.