Not just for Bulgaria, I don't think that any government is accumulating Bitcoin.
Yes, governments are interested in cryptocurrencies and want to know how they could be maybe integrated into state system but they are not buying it, not with funds from state budget. So, don't believe to.everything you read or hear somwhere.
You really didn't read the whole story, didn't you?
Nowhere is written that the government bought bitcoins, they were confiscated during a big police action from bunch of a criminals and were supposedly kept in secret. Some say the government already sold them on private auctions, or never actually had a possession of the private keys of the confiscated wallets.