from what I read, when the Indonesian stepfather adopted him and they moved to Indonesia, his US citizenship was rescinded.
Your source is mistaken.
A minor cannot renounce his American citizenship, nor can others do it for him.
Depending on Indonesian law, it is perhaps true that his parents may have opted for Indonesian citizenship for him.
If that were the case, given dual citizenship, Obama could've renounced his American citizenship when he reached his majority.
There is no evidence, however, that he did.