I noticed the same thing when I re-capped mine. I happened to be looking at the traces and thought something seemed odd, so I measured it and sure enough, the marking on the board is backward. I had already removed the old capacitor so I'm not sure whether it was installed correctly or not.

There is a similar error on the Electrohome G07 monitor used in a lot of 80s arcade games. One of the capacitors is marked backwards on one side of the board and it was never corrected throughout the production run.