To "walk around" means to roam or wander. Most people understand this use of the phrase. Except they clearly didn't mean that the guy roamed Australia, because

To "walk around" means to roam or wander. Most people understand this use of the phrase. Except they clearly didn't mean that the guy roamed Australia, because that's not particularly noteworthy. He "packed his backpack and walked around the entire continent of Australia by the coastline". The grandparent is pedantically correct that well actually you cannot walk around island. Must be fun at parties...