The latter part of what the Bangladesh said;
No legal authority in the world permits such trading, Bangladesh Bank said.
We all know that there are countries that have permitted it and that's why there are exchanges existing and keeps on operating helping users like us to convert and trade our cryptos to cash and vice versa.
A small portion of market cap is contributed from the Bangladesh currency, currently ranked 109th (8,415 BTC)
[1] out of 116 contributing countries. If one assumes these statistics actually reflect the current state of affairs, then there are a number of "illegal transactions" involving more than 8k BTC made by Bangladeshis. This means that there is a loophole in the bitcoin trading ban.
1.
https://fiatmarketcap.com