That's unequivocally a lawful basis for a court-ordered search warrant. They must have probable cause that the person being searched has evidence of a crime; not necessarily that the search target and the criminal suspect are one and the same. Search is investigative; not punitive.
The newsworthy part of this is it's a journalist they raided, and to go after their journalistic sources at that. It's previously been a DoJ policy not to go after the media for things related to their reporting work. But that policy wasn't a legal or constitutional requirement. It's merely something the DoJ voluntarily pledged to stop doing, after the public reaction to President Obama's wiretapping of journalists in 2013,
https://en.wikipedia.org/wiki/2013_Department_of_Justice_inv... ("2013 Department of Justice investigations of reporters")