Can your left pinky ulnar styloid fracture cause middle finger trigger digit?

No the ulnar styloid. Is not directly connected there but if the hand is very swollen froma fracture and the trigger finger was waiting for a reason to become more symptomatioc then the swelling in the hadn could be the tipping point. But a direct cause...Unlikley. Causlality is a tricky issue as we often attribute one problem to another temporally, but you might as well blame a trigger finger on a thunderstorm.
Possible. The fracture itself most likely did not contribute to the trigger finger, though if you were in a cast and/or splint for a prolonged period this could have exacerbated the trigger finger. See your orthopedist for possible injection and evaluation.