The article makes it sound like it was probably cross-country eyeball surveillance, not GPS tracking:
"It's an incredibly complicated, well-choreographed ballet, if I may, of surveillance efforts that would cross multiple FBI field divisions," McCabe said. "Would involve multiple surveillance teams who were following him in certain areas and handing him off to new teams."
Former FBI official explains how agents tracked, surveilled Bryan Kohberger
To put a tracker on the car, they would need a search warrant (Carpenter v. US --Sup. Ct. decision) and I don't think they had probable cause to get a warrant at the start of the trip. JMO.