I've said this in other threads, but I am a firm believer that if a birth parent has not indicated they want contact, the child, even as an adult, needs to leave them Alone. This man may, well probably has a family of his own that knows nothing about you. The fact that he had sex with a woman one time does not give you the right to even try to get into his life.
One should not give advice if one does not know what really goes on. Statistically speaking in the few open provinces and states in North America the amount of birthparents not wanting contact is astronomically small. Now, in this girl's case she should avoid him. He sounds like a bad egg. In Manitoba, of the rounded 50,000 birthmothers only 60 asked for no contact. In Maine, fewer than 1%. In Oregon only .25%.
What you do not realise is the fact that many birthfathers were never told they fathered a child or they were forced to sign, something that still happens in Utah. Birthmothers were brainwashed by adoption agencies, churches, their parents that they "were not real mothers" and "searching for their relinquished child is sinful and interfering with the child's life" etc.
It doesn't matter if his family knows about her or not. She is an adult and has a right to search and any family members of her have the right, as adults, to decide with whom they want or don't want contact with. That isn't up to a father or a mother.
People were not meant to stay in closets.