> I assume you mean that the creator of mIRC was aware of it and encouraging it.

Like most licensed software, it was likely licensed by “US Government” or “Department of Defense”. Plus, it was openly written about back in the day. It was well known. No clauses in their licensing to prevent its use for those purposes.

Comparing to Mattermost and amplifying the original comment, Mattermost website is openly associating with PlatformOne.