Those are almost certainly all using the client functionality. I'm not sure what uses libssh as an ssh server. (Edit: it may be that there is no open source code in existence anywhere which uses libssh in this way, except maybe some sample code. See https://twitter.com/cryptomilk/status/1052286350379114496 )

For some reason that site doesn't seem to list all possibly reverse dependencies of libssh.

According to the brew uses command the possible dependents are ffmpeg, ffmpeg@2.8, hydra, sshtrix, tmate, wireshark, and yafc. I say possible because some of those can optionally depend upon libssh, but the user has to opt-in to building with libssh support.