Just take it as a given. You don't know where he came from and you don't know where he was much of the time.
But if you take into consideration his possible paternity, the fact that he ended up in Indonesia isn't surprising. The question remains, when did he go there and for how long?
Who was Soebarkah?
Yes, it’s really odd how many people take “Dreams” as fact - as given - when even the book itself admits that people are composites and converstations are made up. And the lack of time line is absolutely another tactic to make it seem as though it’s an autobiography when it is not at all. It’s like stage props or stage scenery that can be moved around, flats painted with fake perspective, and so on.
Weren’t the Soebarkah family found at some point?