Income derived, means you work there and generate income there.

Yup, a lot of people misunderstand that if money is come from overseas, it is tax exempted, which is not true.
Company here doing export, also receive payment from overseas but still it is local derived income and subjected to tax here.

It is not about where the money being paid or from, but where the money being generated.

The reason of it is given tax exempted (apart can induce inflow of money), because the income may already taxed at there, so unfair to have double taxation.