You got it... somewhat wrong.

The NSA wiretap has been in effect since about the late 1990s, long before Findsen and Frederiksen held any position on the matter. The Snowden leaks in 2014 revealed this. So in a sense, it was already public knowledge.

But then it was sort of re-leaked around 2020. The accusation is that Findsen and Frederiksen leaked this information to journalists and the public. The watchdog situation is technically a different matter, but the theory is that Findsen is being hit with these accusations of the leaks as revenge for the other thing. Though, I am not sure how true that theory is, but this is how these two things come up as seemingly related.