because they were part of a group of people who were fighting our enemies in Afghanistan at the time - the Russians -
the enemy of our enemy is our friend
you could ask the same question of all the Tamils in Canada who supported the Tigers a terrorist organisation, the Jews who send money to support illegal settlements, the Ukrainians who funnel money to neo Nazi private armies back home , the Sikhs who express support for a separate state in India some of whom were convicted of terrorism
how did they all become Canadian citizens?