Or, more likely, with no understanding at all.

Is that not exactly how a human decides which move to play?

When playing, they have a strategy, which they could explain to other go players. They don't just recognize patterns or do brute-force look-ahead. The same is true for good chess players.

So if the best move has an evaluation of +0.05 and the second best has -0.02 , the difference is probably a very subtle positional improvement (and the first move may not in fact be better; chess programs aren't perfect). If the best is +3.12 and the second is -0.02, and you can't see why, there's a concrete material tactic you're missing (or, less likely, a major, obvious positional devastation).

But, it can't tell you what you're missing, just the magnitude of the difference.

Concept was the same as you describe. No rocket science. I purposely read nothing beforehand, because I wanted to devise an approach and this seemed the most obvious.

Of course, nowadays that is not the only technique in use.

In any case, I'm not sure why you think it impossible to add any additional analysis to the program as it repeatedly scores millions of positions.