Good news, I've found a plausible Walter Ruby in New Jersey for the 1920 census, a good bet to be the young man who will be in a car accident in Jersey City 15 years later. He is Walter Ruby, 25, one of three Ruby-surnamed stepsons of Thomas Fahey of Jersey City Ward 10. This Walter Ruby was born in New Jersey of parents born in New York, like the one from the 1930 census. He is listed as being a clerk with a steel company.
Anyway, it puts to rest the whole double life scenario. Wild goose chase indeed. By the way, it is amazing just how many Walter Rubys there were with birth dates in the 1890s. There are WRs in Nebraska, Kentucky, Alabama, and several other places, in addition to the one in Manhattan and the one in Jersey City.