Nobody is even asking the question if he is an Indonesian citizen who still retains his citizenship.
That issue its all tied up in his passport records, which someone once peeked at but was quickly prosecuted and zotted from the face of the earth.
If he “became” a citizen of Indonesia as a youth, and even if he were adopted by Soetero, after he reached majority he would have to take steps to reclaim his USA citizenship. I am sure he did not do that.
Rather, he sold himself to Occidental College, then Columbia and then Harvard was an exotic foreign student, got all the aide and breaks that entails, etc.