Why is "make" not accepted? I think it is impossible to distinguish between past and present tense with this sentence alone.
Simple present tense should be acceptable since there is no phrase that indicate the timing. If they want to use it the past tense, they can do 'Tadi saya membuat teh' or 'Saya telah membuat teh'.
"I'm making tea without sugar" should be accepted as "membuat" can work for past and present
"I made unsweetened tea" should also be accepted.
Saya membuat teh tanpa gula, rasanya pahit tak seberapa, membuat hati gundah gulana.
Why is this past time ?
it really shouldn't be, membuat doesn't give tense so can technically be past or present but is mostly used for present. really it should have used 'terbuat' for 'made' or 'saya sudah membuat' i already make'