A run on sentence is the one which uses two or more independent clauses and can add more clauses, but the clauses are not joined by any conjunction or joining word or any punctuation mark. For example: he was eating rice he couldn’t understand what to do next.
In this given sentence, the independent clauses are being added without using any punctuation or conjunction. They first went to the aquarium and after that had lunch but it is not joined by any joining word. Therefore it is a typical run on sentence.
