From what I've heard, this is only deployed when the feds come out. However, this is all from word of mouth and I can't be sure about anything lol.

I'd assume it's a firmware backdoor. First, because it works on both platforms, and they both display a locked out message - something you can't do without malicious software already existing on the phone. If it's network stuff like the stringray, it's a protocol exploitation and doesn't require any special software on the phone. But, you also don't get any kind of warning message on the phone - since no software is needed on the endpoint. Unless this is something baked into all the wireless chips all these vendors use, it has to be some kind of firmware backdoor.

It does also show us that the state considers these protests threatening, but if they're willing to reveal this there must also be a large amount of other techniques and backdoors that they haven't revealed yet - exactly like you said. This is also hinted at since this is being deployed semi-frequently - it's commonly brought up as happening when the feds snatch someone off the street. Since we've heard about it from a bunch of people from across the country, it's likely deployed nation-wide and put into use frequently.