How do you know he's guilty of keeping records illegally?

If he kept the records himself that was illegal.
If he has just written them, I am not sure what the misdemeanour would be called.

He can't be guilty of illegally keeping records if there were no records to keep.

The records he has produced are only hand written ones, written by him!

He can only be legally adjudicated to have lied if Green sues him.

Legally I suppose yes, but if it is a lie he would still be a liar.

In any case, if he did glean some proof that he decided to hang on to that the porn existed, how is that illegal?

Because it is illegal for police to do that.

Is leaking illegal?

It can be. Leakers have been aquitted because they acted in the public interest.
Receiving leaks is not at all illegal.

How is that any better than a cop noting Green's pornography supply?

That is a value judgement, but it is still illegal for an officer to do that. There is no supporting evidence that the porn existed.