That's not the mask. That's the map in the channel. The mask is in the layer stack the same as Photoshop. That layer doesn't have a mask. Your mask is applied to the group.
Well, that grunge is not even a mask, it's a fill layer. You can alt-click on the group mask and that will isolate the mask you have there with color selection. If you were to add a Fill layer in the group mask with that specific procedural, then when you alt-click the group mask you would see what you want, the black and…
Perhaps it's user error, but when I alt+click on the procedural grunge, it just displays a dialog box for me to select other procedurals. I can alt+click on the group's mask to display in the viewport but I can't seem to isolate just the procedural?