How the "Get Control Bool" nodes in control rig graph get this boolean?

I am playing with the control rig asset from Metahuman, and this “Get Control Bool” nodes confused me.

How does the “Get Control Bool” node here get this boolean?
I didn’t see any name property under the “Stretch” control (or animation channel) related to
“arm_r_stretch_switch” . I also try to create a new “Get Control Bool” and use the magnifier button to choose the “Stretch” control, and it gets me the same “arm_r_stretch_switch” like magic~

Any ideas or I missed something?

Thank you~