I think what you are looking at is the rail on the slide portion which runs on the inside of the frame and looks like a cut but is the rail. This is visable like this because the dustcover does not extend to the end of the muzzle.
I seem to remember reading on this forum or on Hennings website that he had cut off part of the full dustcover from one of his guns but not sure if it was this one.
He didn't cut the dust cover. EAA doesn't import the sort dust cover model, just the long dust cover model.
When I mentioned cutting off the dust cover, I was referring to the picture shown on his website, which shows a short dust cover and is more than likely an older version, not the pictures shown above on this post.