Don't know what's terms included on the law declaring bitcoin or any other crypto as illegal there but any form of an advertisement on such illegal things is punishable by law at most of the cases. I just wondered how come the owner can freely operate his business? Or maybe like a form of a small protest or rally as part of freedom of speech?
Bitcoin itself isn't banned, you just can't use any foreign currency, and I suppose they put Bitcoin under that umbrella:
The ban comes as an enforcement of sections 4,5 and 8 of the 1947 law that regulate trading in foreign currency without authorization or general permission from the central bank. Section 5 severely restricts payments done outside Bangladesh, which definitely affect bitcoin payments.
You can probably also get away with USD and EUR cafes, except they'll need a special permit to actually accept those for payment lol.