In 2007 Autism was still mainly referred to as Aspergers Syndrome.
Was also nowhere near in the news daily (U.K) as it is now so awareness would be lacking in many quarters.
So I agree he could've felt isolated especially being in a mainstream school.
Whether that made him want to run away and start a new life somewhere I'm not sure.
I can believe on relative spur of the moment he loved Music enough to want to go and see a band in London. His Dad said in an interview they already travelled to different cities to watch music so maybe he just wanted to do it by himself for once?
Same as when kids get to 16-17 they want to go to a music festival together.