Probably *The London Eye Mystery* (2007) by Siobhan Dowd, who passed away the same year.

From [Goodreads][1]:

> Monday, 24 May, 11.32 a.m. **Ted and Kat watch their cousin Salim get on board the London Eye.** He turns and waves and the pod rises from the ground.
>
> Monday, 24 May, 12.02 p.m. The pod lands and the doors open. People exit in all shapes and sizes – but where is Salim?
>
> Ted and his older sister Kat become sleuthing partners since the police are having no luck. Despite their prickly relationship, they overcome their differences to follow a trail of clues across London in a desperate bid to find their cousin. And ultimately **it comes down to Ted, whose brain runs on its own unique operating system,** to find the key to the mystery.

[Google Books][2] offers the following quote about mosher and being cool:

> 'Salim's a mosher, I said.
>
>'A mosher?'
>
>"It's northern for "casual, cool dude", I said. 

---------------

Found with the Google query `book mind "wired differently" "mosher"` which returned
[this page][3], which is taken down, but the Google preview read:

> “The ABC's of Diversity”
>
> A Selective Bibliography of Multicultural Books for Students in Grades 6-12 ... the two siblings must work together-Ted with his brain that is "wired differently".


  [1]: https://www.goodreads.com/book/show/1184305.The_London_Eye_Mystery
  [2]: https://books.google.fr/books?id=jiHLr3_KQyQC&lpg=PP1&pg=PA54
  [3]: http://www.unc.edu/world/2010PartnersWS/ABCsofDiversity6-12.pdf