The point is, Pashtuns did have significant role in contribution towards Islam in Bengal, you cant shrug it off merely as some tribesmen in service of others or products of Turks. Afghan saints and Ulemas also accompanied Afghan rulers and settlers into Bengal.
Most of the Bengalis, do not claim to be descendants of Pashtuns and there is reason for that. In 1614, when Afghan chiefs Bayazid Karrani, Anwar Khan and Usman Khan were defeated by Mughals and they lost their chiefdoms (Sylhet, Baniachang etc), bulk of the Afghans/Pashtuns migrated from Bengal to Deccan Sultanates. Whatever descendants of Pashtuns live in Bengal today, are mostly descendants of Pashtun mansabdars of Mughals who were given jagirs in Bengal. For example Saeed Khan Panni was given Atia Pargana (Tangail district) by Mughal emperor Jehangir and among his descendants are Wajid Ali Khan Panni aka Chand Mian, 'the Bengal's second Muhsin'. From Baharistan Ghaibi, we come to know that two out of three members of advisory board of Mir Jumla, the Mughal governor of Bengal, were Pashtuns/Afghans and Afghan contingents were employed by him for difficult Assam campaigns.
Historical mosque built by Saeed Khan Panni in Atia in 1609