It’s not some brain dead conspiracy theory. The NSA and CIA were using this kind of technology way back in 2004. Imagine what they can do today.

https://slate.com/technology/2013/07/nsa-can-reportedly-track-cellphones-even-when-they-re-turned-off.html

And it isnt just cellphones that could’ve given away the location. Health devices like step counters, headphones, etc can sometimes record location data that gets reincorporated to a device’s location history when the hub device like a cellphone is reconnected. There are many ways to piece together meta data from someone’s devices to paint a complete picture of who they are, where they are/went, and what they were doing (ie, stopped in front of a store display for 20 seconds facing west). Any number of these could be pieced together to identify who was likely in the house.

If he government wanted to hide their methods of discovery (which they’ve been known to do), they could easily piece together the map and say they found evidence of the car passing a banks cameras to justify their investigation pattern without revealing their true method of discovery.

When the San Bernardino shooter’s phone was capture, it was widely reported that they had a back door method to break into encrypted phones but didn’t want to reveal it. They pressured Apple to break open the phone for them and got rebuffed. Then soon after they revealed an Israeli company was able to do it for them, and they got the data they wanted. All of the legal pressure on Apple was an attempt to hide that they already were able to open it but didn’t want to admit it publicly. But they also didn’t have a solid legal/public way to have gotten their information and needed a cover story.

Same happened with Wi-Fi/cell signal hijacking. Government would set up fake cellular hot spots to hijack radio signals and rap lines and location data. https://theintercept.com/2020/07/31/protests-surveillance-stingrays-dirtboxes-phone-tracking/

Now this is extremely unlikely to have been used in a rural Idaho town with no recent murders. But it illustrates that the technology to track a device is very advanced, sometimes not documented or intended by the handset manufacturer, and the government often attempts to deceive the public to hide their methods so they can continue using it as long as they can without public outcry or the arms race of encryption and behavior changes among people who may conduct criminal acts.