They had a very non-specific warrant, something not unlike automatically authorizing anyone who enters a given building to be tagged, followed, and have their homes searched covertly.
Magistrate Judge Theresa C. Buchanan in the Eastern District of Virginia, who signed the warrant used for the NIT, did not respond to questions on whether she understood that the warrant would grant the power to hack anyone who signed up to Playpen, or whether she consulted technical experts before signing it, and her office said not to expect a reply.
So we can't even be sure that a judge knows what she's doing when she's asked to sign a warrant like this. They don't have to prove competence.
Search warrants are not supposed to be that easy.