If the bug was held by a nation state, and their use of it was burned for whatever reason, then the nation state could release it in this manner to sow chaos in lots of fun ways:

1) The entire world of iPhone users

2) The financial markets (Apple suffers)

3) The financial markets (non-Apple benefits)

4) The political sphere (distraction from)

5) Deniability (they got their recording and leaked the bug to deny how)