Why it worked
The humor comes from the contrast between the expectation of English proficiency in the US and the creator's self-deprecating Spanish response, combined with the absurdity of the random English words.
Summary
A person is working at a Subway restaurant and is asked about their English skills. They respond in Spanish, indicating their English is not good, and then jokingly list random English words before saying 'Pues nada' (Well, nothing).