This just shows a fundamental lack of knowledge of Bangladeshi culture. The term "Dhakaiya" is reserved for people who are native to Dhaka district (i.e., যাদের দেশের বাড়ি ঢাকা জেলা). These people also speak a distinct Dhakaiya dialect which stands out just like the Sylheti dialect.
Here is a sample of what Dhakaiyas sound like:
Most inhabitants of Dhaka city, including vast majority of societal elites, are non-Dhakaiyas whose families migrated to Dhaka from other parts of Bangladesh. Calling Bangladeshi elites "Dhakaiyas" and claiming they speak "shuddho bhasha" is therefore comical to say the least.