Yes, it does include them. Two-thirds of Americans aren’t putting any money into 401(k) plans. Only 14% of employers offer them, and less than half of their employees are invested in them.
The idea that everyone, rather than just a minority, is benefitting from stock market gains is fantasy. Spreading the false claim encourages resentment: How come they are getting rich and I’m not? It’s pernicious.
https://www.bloomberg.com/news/articles/2017-02-21/two-thirds-of-americans-aren-t-putting-money-in-their-401-k