I'm not sniper material by a long shot, but I'm a pretty dang good shot through open sights. Crouching right there, the thought of making those shots with a pristine rifle, much less that clunker, looked WAY unlikely. WAY.
Funny. I looked through that same window as you did, and my impressions was just the opposite -- it looked pretty easy to me. The shot was much closer than I had the impression of from looking at photos of the area. Like you, I'm not an 'expert marksman' but even with my limited experience, I think I could hit 2 of 3 at a slow moving target from there.
And there was noting "clunker" about that rifle. It was and remains a fine, accurate weapon. The only reason it was so cheep then ($15 ?) is because there were tens of thousands of them on the surplus market.
We'll have to agree to disagree on the quality of those rifles. I've never fired one but I've had the opportunity to hold and inspect and shuck the action on a couple of 'em in good shape.
MM (in TX)