These are nothing more than wannabe Arab. Even the genetic studies shows that most of the south Asian Muslims are native Muslim converts bear no to very little Arab-Turkic ancestry, it was just a cultural exchange with Central Asia, not the genes.
@ Now, I give you some solid reasons :
1. Bangladesh is a riverine country so this natural barrier gave them an added advantage to the Muslim fugitives of Indian Sub-continents. Delhi was ruled by the Muslims for near about 800 hundred years but if today you go to Delhi and its surrounding you would find hardly 15/20 % are muslims but see here in East Bengal where 90% are muslim. The reason is whenever there were a clash between two muslim dynesties, the looser used to fled and took shelter in Bengal after crossing the mighty rivers. Throughout this 8 centuries the muslims fugitives took shelter in Bengal and settled permanently.
2. Once Turkisk General Ikhtier Uddin Muhammad Baktr Khilji invated Bengal he brought lot of Turkish soldiers (20,000) and after his death his followers also brought lot of Turkish people and were absorved in various administration.
3. It is said that once Changez Khan and later his grandson Halaku invaded Muslim Empire, many Central Asian Muslims along with their belongings migrated in bulk in Northern India. Later on many finally landed in Bengal.
4. Once Ibne Boututa visited Bengal specially Sylhet and then towards Tibat, he was surprizedto see that most of the Sylhet people he thought to be Turkish. As their dresses, houses, food habits resembles Turkey. People says that majority of Sylhet people belongs to Turkish origin. During the times of Hazrat Shah Jalal many Turkish people came and settled in Sylhet. Still there are a gulf of difference between a common Bengali and a Sylheti.
5. My assumption is, the greater people of Rajshahi, Noagaon, Natore, Chapai Nababganj, Maldah belongs to Afhgan origin. Some people says that they are the offsuit of Sher Shah Suri. Well, the fact goeslike this, once Babur invaded Delhi in 1526 at the First Battle of Panipat, the Ibrahim Lodhi (Afghan) was defeated and killed but his Army chief fled away along with some troops and took shelter in Bengal.
6. During the time of Maratha(Shibajee) invassion many muslims who were in Calcatta, Nadia, Bahrampur and oth It is mixtureer southern districts of West Bengal including Orisha came and crossed the Padma river and settled in Bengal.
7. During the times of Ummayet and Abbassit rule many Arabs came and settled in Bengal specially in the coastal areas. The Arab muslims initially who came and settled in Arakan subsequently migrated to Bengal and settled here. Once there were clash between Ummayet and Abbasite dynesty many Ummayet fled and finally settled in Bengal.
8. Once Isa Khan revolted many Mugal soldiers came with Mansingh. These Mughal troops had to fight with the soldiers of Isa Khan and majority were settled in Bengal..
9. After the riot of Calcutta and Bihar many muslims came and settled in East Bengal. After the riot of 1949/1settled 950 the muslims of West Bengal were forcely evicted and were settled in Bengal. In this way around 50/60 lacs of muslims came to East Bengal and finally settled here.
So, finally I want to say that slowly and gradually majority of the people are the foreign muslim origin who came and settled here. It is a mixture of blood. We the Bengali Muslims are a heto-genious nation rather than homogeneous nation. Yes, we have a common thing and that is a religion. These are my practical experiences.