At least they asked for further opinions on this by other researchers:

But some experts urged caution in interpreting the findings. Jacqui Hanley, head of research funding at Alzheimer’s Research UK, said: “Without a detailed picture of what is going on in the brain, we don’t know if being a ‘morning’ or ‘evening’ person affects memory and thinking, or if a decline in cognition is causing changes to sleeping patterns.”

Jessica Chelekis, a senior lecturer in sustainability global value chains and sleep expert at Brunel University London, said there were “important limitations” to the study as the research did not account for education attainment, or include the time of day the cognitive tests were conducted in the results. The main value of the study was challenging stereotypes around sleep, she added.