Because everyone in a team can see what the team has planned. This is intended.
Your hunts list shows every hunt belonging to your teams, including hunts you are not taking part in, so you can see what is happening on the ground and when.
It is not a fault, and nobody's information has been shared by mistake.
You only see hunts from teams you belong to. If somebody sends you a link to a team you are not a member of, you get a message saying you do not have access — you never see the team's contents.