After coming back with the client, Trista was very surprised to see Rein there. She had a very impactful first impression of Rein with his great strength surpassing his own rank. So with that and Rein's extremely handsome face, it was impossible for Trista to forget about him.
Rein also greeted Trista respectfully. Technically they were at the same rank and showing respect for someone like Trista was the right thing to do. Even though Rein knew that he was stronger than her, but that was mostly because he was born as a genius with dual affinity and inherent special abilities. So, for Trista to reach this height without those was truly something she should be respected for.
It was very normal for strong individuals to not put weaker ones in their eyes. It was not considered something rude and was common sense for this world. There were very few people who went out of their way to show respect for someone weaker.