Observations

Imo, Arnold was guilty of something inappropriate with one or several of the children in his computer class because he freely admitted abuse of boys in earlier years. It's a common tactic of the guilty to fess up to crimes they've not been charged or accused of after being arrested for current similar crimes.

He's basically saying, 'Yes, I've been a bad guy in the past, the boys didn't complain, no harm done, and see, I'm an honest guy, I'm owning up and taking responsibility for my past for which you can't jail me.'

Howard has obviously blocked the abuse that Arnold said occurred over several years, and the 2 other boys, one a child of a family friend, have done the same.

There was a lot of hysteria attached to this trial without a doubt, but this documentary was purposefully misleading and with an agenda. The 'victim' reclining on the sofa, a prime example.
The police threw everything at Arnold and Jesse for good reason but it wasn't smart, imo. Some children may have fabricated or embellished their stories, but I'm convinced that Arnold and Jesse were lying too.

This confession by Howard which wasn't included in the doco -

Howard Friedman, in which, according to the report, he said: “Jesse is guilty and you’re going to ask me how I know. Because Arnold told me.” He said Arnold Friedman had confessed that both he and his son had “misbehaved” with children in the class, but it is not clear from his statements what that misbehavior might have entailed.