East Bengal was the south-eastern border of the Eurasian continent-wide Turko-Mongol push:
The Rise of Islam and the Bengal Frontier, 1204
Genetic connection of Arabs and then Turko-Mongols with spread of Islam is a well known fact. Some places the Turkish language became predominant, in other more populous places, the cultural influence became more religious than linguistic.
But nationalism like Pan-Turkism or Pan-Turanism (Bozkurts?) sometimes promote many false and wrong headed ideas and pseudo facts. It was partly responsible for the breakup of Ottoman, by creating Arab nationalism as a reaction, as it is alleged.
Russia is still the winner in CAR's, but if Pakistan, Iran and Turkey can form a closer economic partnership and develop their region, the CAR's Turkics and Mongolians may join up, when this union may look more attractive. For now the Russians still provide jobs for CAR's migrant labor. But the future will be different, I am sure. Russia does not provide warm water port and direct land connection to South and South East Asia or Europe, which the southern Muslim countries provide.