"I have a grandson."
Translation:Saya punya cucu laki-laki.
I said "saya mempunyai cucu laki-laki" but duolingo corrected me with punya instead of mempunyai when they have the same meaning. If anything, mempunyai is more correct because it's more formal and shows that it is a verb that required an object
That's an issue with duolingo Indonesian. Aku & saya mean the same thing (Aku is has javanese roots but saya comes from malay but both are used. In jakarta you will actually hear "gue often which comes from betawi dialect). It's the same thing so you are actually correct. you will run into similar problems with elu/kau/kamu/anda (kamu & elu (betawi roots) is most informal, while kau is still informal but more formal, while Anda is very formal. Although in Indonesian you should always refer to someone of higher rank or age than you in 3rd person regardless)