Where do you live?
In our country, post offices have not only been sending or receiving letters or packages for a long time, but they are offering many more services like health or life insurance, withdrawal of money from bank accounts, Western Union, sale of toys and books, watches and cell phones etc.
So it's not surprising or strange that they've added this new service as well, crypto exchange.
I think that you should change your concept about the business of post offices in some European countries