Or it could already have been included in the calculation. If perhaps there had been 47 people in the room including 6 male virtuists and 5 male non-virtuists, and then Brennan arrives, a male non-virtuist, he makes all the numbers work out with 48 people and 33 virtuists of whom 6 are male (2/11).
But in fact we know it wasn’t, because there are an odd number of people in the room!
He might not know what a Virtuist is—it may be an arbitrary label for the purpose of this test, in which case the answer would not change.
Or it could already have been included in the calculation. If perhaps there had been 47 people in the room including 6 male virtuists and 5 male non-virtuists, and then Brennan arrives, a male non-virtuist, he makes all the numbers work out with 48 people and 33 virtuists of whom 6 are male (2/11).
But in fact we know it wasn’t, because there are an odd number of people in the room!