Given there's no past tense in the Vietnamese, then DO or DID should be correct when translating from Vietnamese to English. Unfortunately the system is too rigid or too simple and DID is marked is incorrect.......... the Level of English here is very very disappointing.
The DL English translation is incorrect. The tense is abnormal. Correct tense would be DID.
The translation is correct, there's no past tense in the Vietnamese version. Now, whether it's a grammatical construction anyone would actually say is another matter entirely.
Where did they hear it? Should be the accepted answer. And though technically no past tense, thấy would imply so being that it indicates a successful ability to do something, in this case hearing something.