I am betting you are part of those groups somewhere or they of yours.... make sure you are not in users just in admin and make sure you and they share no common groups. if say you have and users1 and a users2 group and a third group lets say users3 and a user from users1 is put into users3 he will see all events for all users in users1 and users3 even if there is a user in user2 and user3. Also MODS and ADMIN will see ALL events because they see ALL groups.. create a user and just put him in users2 group and he will only see events for people in users2.
