Unexpected Encounter with Estranged Father After 30 Years

I talk about how my parents divorced when my mom was pregnant with me, and my father gave up all parental rights. I've never met him or spoken to him until about two years ago when I was working at a healthcare facility and saw him scheduled for an appointment in the office next door. We had a brief interaction where he walked into my office, I directed him to the correct office, and later I held the door for him on my way out, and he thanked me. This was the only time I've interacted with my father in my 30 years of living.