Therefore nothing he did as an 18 year old renewing an Indonesian passport compromises his USA citizenship. The USA does not care
I've told you what the law is, and you just ignore it and your counter-argument is just to say crap off the top of your head. You can repeat this 20 times, it doesn't make it any more true.
You ask "how would they know?" As a matter of law, it DOESN'T MATTER if the US knows of it at the time or not.
The expatriation happens BY OPERATION OF LAW. No one has to tell the US government. Obviously, someone can expatriate themselves and get away with it if the US government never finds out. But whether the US government learns of it or not, as a matter of law the expatriation is not dependent on notice to the US government.
Where are you getting this expatriation being automatic even if the USA has no formal knowledge of this crime? Baloney. Who expatriates you then? G-d?