Firstly, yes, you can access workspace variables from within with a GUI. Check out the 'evalin' function. The default workspace is defined as 'base', here's an example of how to use it below:
uiVar = evalin('base', 'workspaceVar')
Secondly, if your curious as to where the variables are coming from when the model is loaded right-click on an empty portion of the Simulink model and then select 'Model Properties'. Under the 'Callbacks' tab I suspect you will find an asterisk symbol next to PreLoadFcn or PostLoadFcn signifying that there is code being run during those events. You should be able to look into that code to figure out where the variable creation is.
Let me know how it works!