That you can set a track for an instrument doesn’t reserve that track exclusively to that instrument no, but if you have assigned a midi device to it, a channel and a track, notes would not be recorded anywhere else when recording with that midi device (not even if the instrument was selected and the cursor is in a different track). So the situation that you show in your image more or less applies.
You can also try this tool out:
http://forum.renoise…gement-console/
It is still beta, but the setup is a bit quicker with this tool, it makes things more obvious and a lot easier to assign several instruments to several different tracks.