I am reporting it as an error, but I am unsure if it is: I had responded "Mimi sinywi bia moto" and it was wrong. Is it incorrect to explicitly include the subject when there is no ambiguity?
No, it's not incorrect. It's just very emphatic. "I don't drink warm beer."
I think "bia (ya) moto" means hot beer. I found you can use the adj. "-vuguvugu" for lukewarm: bia vuguvugu