Either by being the last ones out of the park, being there late enough that almost no one is around, or using super long shutter speeds so than anyone moving through the picture doesn't show up is my guess.
Thanks for you patience and perseverance while taking them! Fog seems to reveal Disneyland's beauty as well as conceal it. Reminds me of a time after returning to the motel room after NYE at Disneyland. The second floor motel landing faced the park (obviously this was before DCA) and my brother and I sat there watched the fog roll in around the park. It was so serene.