Nobody has invested in anything.
It's all related to the 2017 seizure of 200k coins.
https://www.coindesk.com/bulgarian-government-sitting-3-billion-bitcoin
Reheated soup, poor journalism and ...let's see in what mess this thread turns out.
And this article tells that the coins were sold in 2018: https://bitcoinist.com/bulgaria-not-bitcoin-1-6b-finance-minister/
And it 2017 authorities said that they didn't seize any coins: https://emerging-europe.com/news/bulgarias-bitcoin-mystery/
And some suspect that it's a misunderstanding, that comma might have been a decimal separator, so Bulgaria seized only 200 Bitcoins: https://news.bitstarz.com/whats-the-story-behind-bulgarias-missing-bitcoins