I find that if one Googles SECOPS the "meaning" includes information technology. I confess that in my course of information security management at the Naval Postgraduate School to O-3s and O-4s I did teach SECOPS. However, the concept dates from when the only information technologies of interest were paper, telegraphy, telephone, and radio, long before we had invented the term "information technology."
In the first armed conflict of my life, known colloquially as WWII, we taught "Loose lips sink ships." One does not repeat many things that one learns in the course of one's job.
We taught not media but content. What information did we want to keep secret; media was hardly even thought of. Even as I taught it, it was about what those who were to carry out the "operation" had to know about it and the potential for them to leak it. At the O-4 level, it hardly occurred to us that the Secretary of Defense and his peers and colleagues were part of the operation and a potential source of a leak.
The association with IT deals with the porous nature of IT and the potential for adversaries to learn the content from our leaky media.
Let us start from the non-IT meaning of SECOPS, any "information about a military operation is born classified as SECRET, regardless of whether or not it is ever recorded or shared. At the "operational" level, O-3 and 0-4, your life may depend upon the continued secrecy of what you must know to carry out your mission. Therefore, such information is born SECRET; one must share that information, by whatever means, only on a "need to know" basis. Said another way, if the sharing is not essential to the success of the mission, then do not share.
Add modern recording and sharing technology to the equation; just think "chat" in its many forms. Many implementations of chat, including iMessage, Signal, WhatsApp, and, more recently, RCS. provide device to device encryption. In the network, the traffic is encrypted. However, it is in "clear text" on every device in the group. The more participants, the greater the probability that the content will leak, or even that one or more of the devices in the group have been compromised.
Most implementations of multi-party chat, like Signal, will enable any member of the group to see the identifier of the sender of any message. However, the larger the group the less likely that every member will know, or even recognize, every other member (Oh! That Jeffrey Archer). Moreover because of the limits of the screen they may see the identities of all the members of the group only upon request rather than by default. We call silent members lurkers.
Said another way, multi-party chat is not considered to be sufficiently secure for SECRET data.
In the Second World War, the British were reluctant to share intelligence with us because they feared that we might leak. Our Wave Bombe operators, who never told anyone what they had done during the war, were shocked, when after forty years the Brits began to talk about ULTRA. 9/11 happened in part because the CIA and the FBI did not trust the others security. The consequences of Signal Gate will include a loss of trust and a reluctance to share vital intelligence.
Most of those with any knowledge about a military mission will have been indoctrinated in operational security, both in training and experience. Here we had a case of novices, those who did not have experience, who had not grown up in the tradition of SECOPS.