I'm not who you're responding to, so I don't know what they intended. But sleep issues can certainly lead to memory issues. So, maybe both?
When I was in my mid 30s, I suddenly had extreme memory issues. For example, at dinner time, I had no memory of what I ate for lunch or even if I had lunch at all. I could remember people that I knew, but I could not remember if I talked with them earlier in the day. It was all very scary.
After various neurological tests showed nothing unusual, my doctor thought we should look into sleep issues. It turned out I suffer from something called Delayed Sleep Phase Syndrome - whereas the average person has a natural bedtime that is ~24 hours after they last went to sleep, mine was significantly longer than 24 hours.
My doctor concluded that this was the source of my memory issues. That confused me a bit, as I experienced trouble sleeping my entire life prior to this diagnosis. She explained that the consequences of inadequate sleep worsen as we age.
It was inconvenient for work and social things, but I was able to start living longer days (i.e., don't go to bed until I'm sleepy). Within a week, the recall issues I'd had were a memory (see what I did there?). I was also able to fall asleep much more quickly than I had before, and sleep duration didn't have the wild swings I'd experienced all my life.
