Translation:I'm not hungry; I'm thirsty.
The 好喝 Word Bank tile is silent and as usual has been silent for the whole session. Even though it's not needed for this answer, I want to hear it anyway. It certainly makes the other questions intolerable, I'm so sick of this I'm dropping duolingo Mandarin. Please inform firstname.lastname@example.org if they ever fix it.
I think this is the first time I have seen Duo use a semi-colon instead of a comma splice (the latter being ungrammatical in English). So in this situation the semi-colon in the answer given is actually proper English I believe. This is because the second clause is linked to the first and balances it. A conjunction is not required if the semi-colon is correctly used as it is here.
Using a conjunction is also an option but if you are going to use a conjunction such as "but" to join the two independent clauses the semi-colon is not required.