It was as if Tyrol was saying "I too have done terrible things... and I am worse than you, because I am a cylon."
I think a couple of things contributed to that moment. First, Tyrol was close to shooting himself and when Baltar showed up, looked to be in deep thought about what to do next. Second, Baltar had walked into the room without any protection and Tyrol clearly had a gun in close reach, yet Baltar did not flinch. I think that said to Tyrol that this is a man not trying to sell him anything. He believed Baltar was there to apologize. And third, when Baltar admitted to his wrongdoing, I think that Tyrol felt as if he was confessing for him as well.
We are very forgiving of those who admit to their mistakes. We are even more forgiving when we know that deep inside we have our own mistakes for which to answer.
The greatest trick the Devil ever pulled was convincing the world he didn't exist. And like that, poof. He's gone. -- Verbal Kint