I'm confused about this. At my current level of learning, cái ca means mug. I haven't learnt that it also means cup, only that it means mug. The first time I did this translation, I put "The fish bites the mug." I thought it was correct. But, it said I used the wrong word, the right translation was cup. The second time I did it, I used the word cup instead of mug. It said I was right. On this page, it said the right translation is mug. So it is contradicting itself in which is the right answer. Ummm... problem here?
I am Vietnamese. I believe this example just wants to help you memorize two words (con cá, cái ca) and help you practice good Vietnamese pronunciation (this is a popular pronunciation practice when learning Vietnamese, in the old days we study the same way. You don't have to think too much about the meaning of the sentence).
I think since this section only focuses on providing some vocabulary and practicing clear pronunciation, the examples given are just to make the impression that you can memorize them. You do not have to think too much about the meaning of the sentence, just memorize the vocabulary and its pronunciation