Translation:It is cold, I want to eat hot and sour soup.
The 'a' is okay, as here 'soup' can be uncountable (soup in unspecified amount) or countable (a portion of soup). Just like you can drink beer or drink a beer: both are correct and each of them means something a little different. I would believe this particular sentence can be understood in both ways.
There's nothing wrong with drinking soup in English. It just means you aren't using a spoon. It's unusual, so I agree that eat should be the standard translation, but it's not an alien concept to drink soup in English. We always drink the broth at the end, once all the chunks are fished out.
One is the normal name in English. The other is the literal translation of the Chinese.
There are quite a few non-native English speakers using this English-Chinese course, and they typically don't realise that English has fixed orders for certain names and combinations.
'a' is redundant at best (Chinese is heavily contextualized) as we know at minimum this person will drink one non-specified soup, but it is limiting at worst, as now he is stuck only drinking a single serving, or if there is one right in front of him an omission of 'the' as a qualifier or just leaving it out discounts is being consumed.
If we are directly translating, then 酸辣 is "sour and hot". I couldnt remember which word we put in front for English, so I wrote "sour and hot soup", which was counted wrong. I think this should be one of those acceptable mistakes, like a mispelled word, that is counted correct with a gentle reminder.