This is correct. Even a simple charter jet will be using an HSI slaved remotely to a gyro and a flux compass over wires.
An airliner will be using a FMS (Flight Management System) that takes info from the VOR/DME radios, Inertial Reference System (if it has one) and/or GPS receiver (if it has one). The FMS controls the autopilot. TCAS receivers in the tail give alerts. All of this is wired together and susceptible to interference.
Frankly, because reporters are lazy. Those who are pilots and/or engineers have long known about ASRS and interference reports. You can tell from the wording that some of the incidents really shook up the pilots. The problem is, again, that it's so hard to prove and/or prevent.
No, bringing up outside interference is a popular misconception, You see, an airline fuselage is a pretty good Faraday cage. Except for holes, signals do not get in or out. Ever try to use a handheld radio or GPS on an airliner? You have to get very close to a window to get an external signal at all.
The bigger danger always comes from inside the aircraft tube. Which brings up a couple of more common questions which I only have a few seconds to address right now:
Q. My device doesn't transmit. How can it be a problem? A. Almost all modern electronic devices are transmitters of some sort, because they have high frequency clocks to drive the CPUs. Even a toy.
Q. Some airplanes have onboard wifi or cell. How is that possible? A. First, each class and type and model of aircraft must be tested individually. That costs. Second, it relies on devices following basic rules about transmit power. E.g. a device should only have to use its lowest power setting to talk to a hotspot inside the aircraft a few dozen feet away. If there is a software bug (which is not unknown), a device could ramp up to very high power output and cause interference. (That's what happened in the Boeing test case.) This is also why it's dumb to leave your cell phone on in a plane.. it's going to ramp up power trying to talk to a tower, and use battery like crazy.