It seems the tax office is interpreting that as.. money received by someone employed by an Indonesian entity, whether or not the money comes from inside or outside Indonesia. So let's say an employee of Garuda is seconded to Singapore, the income from outside (ie the work in Singapore) is still covered by this law. But if a person (such as harmonykorine) has no taxpayer status to begin with, then they are not required to have a TIN (hence cannot pay tax).
Not sure this is a correct interpretation, but if that is how they interpret it, then I guess that's the end of discussion.
But apparently not all of them interpret it that way. Recently it was reported in this forum that people got in trouble for not reporting rental income obtained abroad:
I know a friend who got "caught" by the Indonesian tax authorities for income on rental properties they own outside of Indonesia. It happened last year - they had to pay a fine and this year they are paying Indonesian tax on their "worldwide" income (not just Indonesian income).
Again it seems that legal certainty is hard to obtain in Indonesia...