"Does the verb "call on" mean to allow reporters to ask questions?"
Essentially, yes.
Given the number of press conferences he's done, I'd say that only one in which he didn't call on females is consistent with chance. Of course, some would say that he's obliged to call of 50:50 males and females. His own Press Secretary is a woman. Maybe on the day in question all the women there came from what Trump claims is fake-media.

Student or Learner