Could be, I guess. But the guy is shooting with a F-100. So, I "pulled" a couple of my Nikkors off the shelf to look at them before posting - and none of them had flat front elements.
What kind of "light gathering" would be achieved from a flat front element?
My thinking is that there is a filter on the front. Could be wrong - but....
I have a 55m f/3.5 Micro-Nikkor that appears to have a flat front element - of course it might not be perfectly flat, but I'm not going to run my finger across it to check. Just because the front surface is flat, doesn't mean the lens element is flat - it is entirely possible to have a plano-convex or plano-concave lens with the curved surface facing in and the flat surface facing out.