I'm a grad student in the US, I have more free time than this. I also had more free time when I was working (even more than I do now). I know very few people that have this little amount of time, and that generally is because they decide that they want to spend their time doing work.

Do you have children? If you have children, you can easily wind up with negative free hours per day.

If you averaged say, 4 parents and 4 non-parents free time, I could see how someone would easily arrive at a number where the "average American has just 4 hours of free time per week"