You could have said this:

"I am the one who hired Preston. Whatever he has done in the past, I have all the evidence in the world in front of me to assure me that he has a transformed heart."

Instead, you had to drag down others, the people who you haven't blessed with your benevolence.

"It is not a common thing to see."

You are being praised for showing kindness to one of us (a nerd, a programmer) while disparaging the others. You can show kindness to Preston without condemning the others. Ask ChatGPT to explain exceptionalism to you if you still do not understand. Every person in prison is a person who can change given the opportunity.

Preston isn't uncommon, Preston isn't rare or exceptional, Preston is the average prisoner: someone who, when given an opportunity, has been able to reform. You can celebrate Preston without disparaging his less fortunate cellmates.

The only rare thing here is that he was given an opportunity (and for that you should be praised).

That is the good faith reading. The comment isn't open to interpretation. What could the meaning be if not that Preston is an uncommon example of a prisoner?

I'm saying that the judgement of a court is useless when making a personal judgement because what a court sets out to do is different to what a human sets out to do. The court system is a collection of complicated and convoluted standards and rules and regulations designed specifically to support a system responsible for depriving people of their rights. A court judgement is not "better" than a human judgement, quite the opposite, a court judgement is often worse, because court judgements are formed without access to all information. A jury for example will often have very important information withheld from them because it doesn't satisfy some esoteric court standard. A person would use that information to form a judgement.

I'm responding to the claim that it's uncommon for someone in prison to have a good heart.

My assertion is that "innocent until proven guilty" is a legal standard that applies to the courts because a system needs standards. People have the luxury of being able to use their judgement. My assertion is that choosing to defer to a legal standard (not proven guilty therefore innocent) is choosing to opt-out of your wonderful human ability to form a judgement based on a lot more than just one single data point.

The person you love comes to you and tells you that they've been attacked by your shady friend. Do you defend your friend from the accusation because "they're innocent until proven guilty" or do you use your judgement and decide that the person you love is telling the truth because you have a lifetime of trust in them?