Why dpreview switched from 50/1.4 to 50/1.8 in latest Sony tests

It's a pity that Sony does not have a good 50mm prime.

There is a flock of hair in the lower right corner on the Studio scene between a robot and a watch, and when compared with Nikkor 50/1.4G, it's a complete mess even at ISO 100. For me it also looks a little sharper on A580 than on A57.

Is it caused by lens or what? If by lens, then people compare lens performance and not camera ISO performance in this test.