Depends how the word daydream is defined.
For some reason, I tend to absorb exterior images - what my physical eyes see in a day - in a grocery store - in a room vs internal imaging such as daydreaming.
For example, I am not a kind of person who can retire at night, have a dream, then wake up in the morning, writing that dream into a short story, even a book, as Robert Lewis Stevenson said he did as I recall.
Also, stick a blank art canvas in front of me and I have to make a conscious effort to determine what I might paint on that blank canvas. For me, it is a labored art process due in part to something which is called constructional apraxia.
Because of the above, I really have not had a problem trying to determine what I may have imagined and what I likely saw. It comes down often to what I saw since I did not engage my imagination.
Also, many years ago I decided to ignore part of how the imagination can be used since I found it was too easy for a teacher/whatever to try to engage the imagination and I decided to kind of observe what the process was vs let my mind participate in the process automatically.
Today I am very aware that some artists like movie directors have extraordinary strong imaginations where they can turn almost endless ideas in their brains/minds/heads into stories for the screen through a process of daydreaming of sorts. These theatre directors can turn vivid daydreams into films which last ninety minutes plus.
It's an interesting topic.