Jasper (Scout, to Kenneth) had watched Arlo packing up - she was experienced enough, had experienced enough, to know when a person was going to start moving. And Arlo was going to be moving. So, just in case, Jasper took it upon herself to follow him to make sure he didn't get into any trouble. He didn't look like one of those guys who would deal well in the wilderness unless he had an awesome support structure to return too, and he might get lost, anyway.
The biggest difference was that Jasper didn't bring much with her - she didn't need it. He might've, but Jasper was used to going without.