Like you said, they didn't look at CS or engineering so your theory isn't supported by data either.

My universty/department's policy is to provide 2 hours of work per credit hour, and the students certainly claim to be spending even more than that! (The truth is likely somewhere in the middle.)

Good point about not being in session year round. It is fairly common to either take summer courses or to do an internship though, which I strongly encourage my students to do! Personally, I took summer courses every year of undergrad and did 5 internships in grad school.

It also doesn’t include the full schedule. Break weeks, summers off, semester breaks, etc. - months of the year, all of which Lambda School doesn’t have.