Does pre-ejaculation leads to pregnancy.

This is a scenario desipated by my friend. She and her boyfriend were fooling around. He was aroused a little ( breathing fast)when they kissed and moved his hands on her( just upper part).While doing this physical actions she had leaned on his lap. (Her lower back was touching his lap ). He was wearing grey sweatpants and she was in her jeans. According to her she didn't spot any ejaculation or pre-cum on his pants. Her main concern is that, is it possible to ejaculate by just being little aroused, if ejaculated is it possible that his ejaculated clothing touch her lower back( top was lifted a little)..if so is it possible for ejaculated semen to flow from lower back or hip to all the way to down. She is deeply worried thinking that it would lead to pregnancy. This happened on April 6th. Her period was due on (April17). Now the period is delayed. Is she just being paranoid and, Can this be the reason for delayed period. Her previous period dates were Dec 10, Jan 9, Feb 11, March 17.