Translation:This sweater is not new.
Not necessarily. Just because it's not brand new fresh from the store doesn't mean it's old and ragged quite yet!
I translate この in "this" and is wrong I translet it in "these" and is wrong too. Why?
What was the full sentence? It appears to me that この wasn't the problem in the translation, as it should mean "this" in this sentence.
At least on my end it seems like the あ in 新し is not pronounced on the audio. Is this intentional?