its not a ban

its a memo,
a mmo that say that the central bank of sri lanka will not be held accountable for any actions done by businesses and that the central bank does not insure or licence it.

.. the central bank doe not endors or licence baked beans.. thats why you dont see a bank slling baked beans.
until there is a GOVERNMENT LAW. that states it is illegal to operate a crypto business. and that law mentions the penalty.. then just treat the memo as what it is .. a memo

nearly every country has released an investor warning memo that investing in crypto is risky and a bank will not insure losses