I felt the same way. It's not just that it's the last currently known sighting, it's the body language.
I don't know enough to analyse it, but the hands in the pockets seems to be from feeling cold. He's looking behind him, though, not like he's looking for a place to pee or to make sure there's no one watching...there's a sense of discomfort from the way he's looking around. Why is he looking behind him from the direction he's just come from? He must know there's no one down there, so why look backwards like that?
I also agree about there possibly being a limp, not a bad limp but consistent with something like ricking your ankle?
And his head is down...why are his head and shoulders so low. Why is he not head high, shoulders high? He knows this place well...if he's looking around for a place to pee, there should be more knowledge and confidence...but he looks scared in a way that makes me feel so sick for his mum to watch that footage.
He doesn't look like the confident young man I expected, he looks very wary and uncomfortable. But if there was no one around, why would he feel that way? He looks sad, miserable, not like "ahh that was a heavy night, now let's get on with walking back to base!" This is really the exact opposite of what I expected to see. Even people who've had too much to drink look forwards as they stagger around. Maybe as he comes into view there's something like a gotta pee bounce, but after that his walk is open yet with that thing that suggests a limp.