The study appears to have used face-to-face courses, to which recorded lectures were added. The researchers did not offer the students a purpose designed online course.
The question the researchers asked, if recorded lectures are better than face-to-face ones, shows the unhealthy fixation with "lectures" which many academics have. Video recordings of lectures are the least useful part of online education, but then "lectures" are the least useful part of an on-campus education.
Trenholm, S., Hajek, B., Robinson, C. L., Chinnappan, M., Albrecht, A., & Ashman, H. (2018). Investigating undergraduate mathematics learners’ cognitive engagement with recorded lecture videos. International Journal of Mathematical Education in Science and Technology, 1-22. URL https://www.tandfonline.com/doi/abs/10.1080/0020739X.2018.1458339