What do dogs do when they run away?

Ok so earlier I let my dog out and i told my brother to let him in and went to my room and did homework. Well my dog never barked to come in so my brother never thought to and thats understandable. The reason my dog didnt bark is he ran away and came back like 45 minutes later all dirty. Also earlier tonight he threw up all over the carpet. Does he think he can do anything he wants when my mom and dad leave town??