I hope this isn’t true. Signal is in the ways that matter compromised by US national intelligence. They demand phone numbers to sign-up and though it’s possible they can’t read the messages they know who is talking to whom and that’s far more interesting to intelligence and drone targeting.
Because with that you find someone using it who is a known member of Ansar Allah, you then find who they’re talking to, those are also probable members or supporters of the movement and you find who those people are talking to and suddenly you have a network of people to drone strike along with their phone numbers which can be used with hacking of cell networks to reliably pin-point their location.
This is bad opsec and I almost think this whole press person added accidentally thing may be an op to get more people aware of Signal and on it as opposed to other platforms.
Honestly I wouldn’t use technology. I’d avoid it as much as possible. I’d go to meetings in person without phone and make sure everyone else does the same. I’d arrange future meetings in person with hand signals to draw the person out of a room with electronic devices into one without before discussing the when, where, and why.
Just so many ways for it to be used against you by the empire with their hacking of telecoms and devices.