The comment for "control.ssh.user" in "ssh.conf" is misleading.  The valid
forms for "service.sshd.contact.string" are indeed this:

#     <hostname>
#     <hostname>:<port>
#     <user>@<hostname>
#     <user>@<hostname>:<port>

But for "control.ssh.user" only a <user> can be supplied if you want to
override the implicit "same user" behavior that happens when leaving the
configuration blank.

copy+paste mistake with the examples.