Nope, this is why I reported it. It' It's "just plain" USB keyboard, recognized by ext* as "USB-compliant keyboard". Normally, when I connect mouse (or mouse and keyboard via HUB, or keyboard with trackball) I got appropriate message.

Unless, of course, unspecified (by extkb database) "USB-Compliant" keyboard got "mouse-mode" enabled by default, just in case there may be trackball. That might be sane explanation (and approach). Anyway, it's indeed no big deal