Non-neurotypical people rarely have totally normal posture and movement, especially if they suffer from sensory processing disorder or proprioceptive problems, which have EXTREMELY high co-morbidity with autism spectrum disorders.
IOW, people that move weird ARE weird, unless suffering froma physical injury that they're compensating for. That's a little bit of a broad brush, but it holds pretty true. I'm a student of human posture and movement, I notice posture and movement a LOT more than most people.
If you think I'm srong about him, message him and ask if he's been diagnosed with any autism spectrum or related disorders. And don't call me mate, please. I find it offensive.