De + el = del. Only the masculine de+el gets contracted to del. If it were feminine, eg. bicicleta instead of autobus, then it would be de la bicicleta.
why is it parade del autobus, but in another question it's estacion de autobuses, and marks del wrong?
Did anyone explain the reason behind your question? I've been wondering the same thing.
A bus station and a bus stop are two different things. A bus station is usually centrally located in a city where all of the city busses stop and you can change busses to connect to a different route. A bus stop is where a bus stops on its route to pick passengers up and drop them off near a select destination.