>that he had lost his citizenship when his biological mother married Lolo Soetoro, a citizen of Indonesia.
I don't believe a minor child can lose right to US citizenship. In rare cases at 16 or 17 per request and review, but at only at 18 child can officially give up US citizenship. Parents can't do it for a minor child.
Other thing is, Indonesia can't determine US citizenship law. They can tell an Indonesian citizen that taking on another citizenship revokes their Indonesian citizenship, but they can't say that taking on an Indonesian citizenship revokes US citizenship. The US citizen seeking Indonesian citizenship would have to agree to formally renounce US citizenship if they wanted an Indonesian citizenship, if Indonesia doesn't allow dual citizenship. America has no multi-citizenship laws, AFAIK.
tl;dr A minor child can't formally renounce US citizenship through his/her parents.
That's what I think, anyway.