this results from the FlexBE App configuration. As you wrote, you added ~/catkin_ws/src/flexbe_behavior_engine/flexbe_states to the "State Library" panel.
Correct would be in this case: ~/catkin_ws/src/flexbe_behavior_engine/flexbe_states/src/flexbe_states (see installation guidelines on the homepage: "Make sure to add the folder which contains the states, not the ROS package itself (i.e. ... /flexbe_behavior_engine/flexbe_states/src/flexbe_states)".