The parent poster is right though, signal is permitted and encouraged for any discussion that would’ve happened over SMS, the issues are somebody dropping details into a channel meant for planning a meeting, as well as somebody accidentally adding somebody that should not have been there.
We do not know for sure but this would be very unlikely. Several of the participants does not need to know this information and it should be compartmentalized.
Information concerning capability or location should not come near unclassified networks or civilian phones. Somebody could drop or steal that phone or glance over a shoulder which could necessitate cancelling the operation or much worse.
