Thanks for the clarification. Of course there's nothing wrong with buying bonds in a secondary market - it is just more risky.If "your understanding" is based on local newspapers it is a wrong one. Blackrock manages multiple investment funds, in particular they run iShares ETF family. They buy things at market price, they sell things at market price and collect a management fee. Ultimate investors are people (or companies) who buy stakes in these funds. This is not really relevant, but they bought Arg bonds during Macri government at higher prices and now are taking a loss.
And there is nothing wrong with buying bonds on a secondary market, by the way.
Many Argentines I know got burnt with these bonds, and are now willing to settle for whatever they can get. They believed in Macri, as many of us did - what a sad disappointment that turned out to be.