It's important when doing these kinds of analyses to consider the effects of DST.

The first graph in the article depicts April 2, 2019 sleep times vs April 7, 2020. But April 2 was just a day after the time change (Dec 31 2019), while the 2020 week was eight days after (Dec 29 2020).

How people adjust to the time change, given the ability to sleep in, is a very interesting topic. But it is different than a description of overall sleep, and it should be a separate analysis.