Logically it is perfect but literally it is not good. Your sentence means "senki nincs a busznál". Duolingo translates the sample sentences literally.
Could you also translate this like: "There are no people around the bus." ?
There is a Hungarian word for "around": "körül". So.... I guess that would be a different sentence.
"Nincsenek emberek a busz körül."
nobody is 'senki', so even though your sentence has the same overall meaning it is a bit different.