He could do his job effectively by asking for more information about what Tor is. This understanding may impact his decision to issue the warrant. Law enforcement lied by omission, do you think they would take that risk if they thought the outcome would stay the same?
They provided enough evidence to the judge to convince him that there was child pron at this location. I'm not sure how knowing there is a TOR node would have made much of a difference.
The difference is that the decision would be in the hands of the judge instead of law enforcement. The balance of power would be in check.
He might have found the grounds for issuing the warrant inadequate.