You didn’t, but the study did talk about people skipping class, probably do to over sleeping.
It can’t say that a 9am class in a system of 9am to 5pm would have better performance at 9am, and it certainly can’t say that the system as a whole would have better performance. Maybe 5pm is too late and affects child care or dinner or night jobs and now students are distracted all over again.
Your speculations have nothing to do with anything in the study, depend on facts that are not supported by any research, and are contradicted by other studies on this topic.