There are many meteorologic factors that can cause strange phenomena on the lake. One that happens frequently is the passage of small, low air pressure cells across the lake's surface. this can cause an upwelling of the surface elevation beneath the low while surrounding higher pressure areas, perhaps miles away, exert a downward force on the lake's surface.
We've seen instances where this effect has caused cold water upwellings in the Central Basin. We'll never know for sure what caused the wave you saw, but this air pressure effect is an example of one possible, realistic source.