Birth Parent Paternity

OK, this is a strange thing for me to talk about but I could use some opinion. I am a 'birth' father. I dated a girl back in the late 1990's and ultimately she became pregnant. Without going into too much detail, we were always careful about accidental conception. But on one particular occasion, she was adamant that we should skip 'safety measures' and that she, in fact, was unable to get pregnant from a prior trauma. Like the 18 year old I was, I went along with things. We decided on adoption as we were both way too young and had not been dating very long. We continued to see each other through the pregnancy, selected and met adoptive parents, and tried to do the right thing. My own parents were very involved, recognizing the sensitivity of teenage pregnancy and adoption. My mother was at the hospital when the baby (boy) was born and briefly saw him before he went home with his new family. I learned of his first name and never forgot it. Since then I married a wonderful gal and we have three beautiful children, all of which are adopted through the very same agency I used as a teenager. My wife and I struggled with fertility throughout our marriage but it was kinda cool for me to come full circle. Around 2017, my mother was digging through some old files and came across some legal paperwork from my teenage adoption experience. She called me and told me my biological son's last name. In today's world of social media it wasn't hard to find him and peek in on his life, however, I was shocked to discover that he looked nothing like me. I could see a lot of his bio-mom's traits in him as well as traits from my late 90's roommate. My wife is quite aware of this story and how much it's affected my life. Maybe I put too much weight on the idea that I had one biological child somewhere "out there", but the possibility of this boy not being biologically mine actually messed me up a bit. It was such a HUGE part of who I am today, having been a birthfather. I did reach out to the birth mom on social media and asked if there was a chance that 'he' wasn't mine and I was ghosted. No response or anything. So last week, the adoption agency called me out of of the blue and said that my bio-son is interested in making contact. I told them I would welcome the opportunity to meet him and answer any questions he has. In a way, I really do want to be his bio-dad but do not want to stand in the way of his search for his bio-dad, albeit me or my old roommate (or someone else for that matter). I could suggest a paternity test or something like that. Any advice (especially from someone who was adopted and sought after their birth parents) would be amazing.