I can confirm your results.
On my LCIII, C22's negative terminal goes to GND, and the positive terminal goes to the PSU's -5V. And the cap matches the silkscreening, meaning the positive terminal matches the + on the silkscreen.
On my LCIII, C22's negative terminal goes to GND, and the positive terminal goes to the PSU's -5V. And the cap matches the silkscreening, meaning the positive terminal matches the + on the silkscreen.