He was shot in the back, after having been bombed- and was found under a pile of rubble. The other man found alive was summarily executed.
The grenade parts found were probably American (reports were changed). The case will be reviewed by the Supreme Court.
However, the monies paid and the apology were because he was not given a fair trial, was imprisoned and tortured for years in Guantanamo. The SCC ruled on this. He was NOT brought home 'at the earliest date", as you stated- that would have been in 2010 when the British and Australian prisoners in Guantanamo were repatriated- and were given varying amounts of payments. 
The original lawsuit posed then was around $100,000. Harper's government spend five million fighting the case.
Sine coming home, Khadr has worked extremely hard to turn his life around. He was deprived of an education- first by his family, and then by being imprisoned- but has been working on completing secondary school and wants to be trained as a nurse.