Seemed a bit way out at first glance to me too.
My 1952 collapsable Summicron 50mm f2 had a bit of fogginess when I bought it used in 1999. A trip to Sherry Krauter at Golden Touch in New York and it is clear again. It may be that the fogging was from lubricant outgassing or some such as mentioned upthread. I like the images that come from the lens, especially with people.
As to the overall performance of 50mm f2 lenses in general, I cannot tell a lot of difference between the Summicron, a Nikkor H, and a Jupiter 8, all of which I use regularly.
F, F2, M3, Kiev 4a