Screen Sharing with VNC -- is it on?
You are safe. Anyone that requests vnc://192.168.1.100 has to enter both an existing user name and the matching password for that user. 

If you enable the anyone may request, then the incoming request is shown and you make the choice to enable the sharing. Until you accept, no view happens.

If you enable the VNC password then it's like a guest account where the user name is not checked but that password will show the screen contents.