A fined tuned argument.....Heywood style.

[Alex K]

The principle of indifference states that if the n possibilities are indistinguishable except for their names, then each possibility should be assigned a probability equal to 1/n.

Since you're now claiming we have additional information (that B could be caused by an intellect), then the Principle of Indifference no longer applies (indeed, never applied, as we have many ways of distinguishing these alternatives). So you've just eliminated the Principle of Indifference as a valid rule for applying probabilities, so you cannot any longer say that the probabilities should be assigned 50 / 50 on that basis. You never could. You've misapplied the Principle of Indifference.

^ Exactely