Each gun is firing once, and you are pulling two triggers. You are just pulling them both at the same time.
but I have to wonder, how does the left gun eject?
I thought some SXS fired one barrel with front trigger then other with rear but if you tripped the rear first, it was both barrels.
Not if the gun is in proper working order. Now what usually happens when this seems to occur is that the shooter is pulling the other trigger without consciously realizing it.