This depends on the sharing level of your network. If you have set the sharing to ‘Open’, then all other mobile devices within Bluetooth range can have the possibility to control your luminaires. However, they cannot change the actual programming (scenes, timers etc.).
If you have set any other sharing option for your network, other people need to know at least a password in order to be able to control your luminaires.
You can find more information about sharing a network here: http://support.casambi.com/support/solutions/articles/12000021618-networks-and-sharing.
When creating a new network the default setting is ‘Not Shared’.