Hey EB.
The player who has connected to your tunnel should have asked for your permission before connecting to your tunnel, especially as you say it has a (planned) design.
If you are not okay with this, then I would ask you not to block it up yet, but put some signs up asking for this player to either speak to you about it, or for them to ask for a separate connection to the nearest hub - in this case, Savannah Hub.
Speak to me/another Zriend in-game if you have any more questions about it.
-SneakySkeleton
Also, I will update the Nether post with these rules, and add rules regarding connecting to community tunnels as was discussed at the council meeting.