As I understand it the selection of doffs is random, but because the underlying pool from which doffs are randomly selected is not equally distributed over all types, the types that are overrepresented in the pool, will also be overrepresented in the final drops.
In this case the pool contains little or no sensor/security officers and an abundance of warfare officers; this imbalance will also be reflected in a (sufficiently large) random selection.
The pool was probably compiled manually with the emphasis on new types like the warfare specialists and doffs of the pre-existing types just thrown into the pool to ensure there s enough useless stuff in there.. I suspect the pool used for the fleet vendor uses only a small subset of the doff's available through the pre-existing channels, certainly if it was compiled manually..
i just got a flight deck officer blue an a purple science boff
just rember when new bound to be issisue with stuff