Ghost Notes
Ghost notes are notes that don't appear to be following anything, or technically cannot be following any instrument track in context with the chart. Keep in mind that this term has a particular connotation associated with it, as ghost notes are often referred to in a negative way because of how they impact a chart, although there can most certainly be intentional uses of it as a technique in charting.
The reason why ghost notes can be an effective technique to use despite not actually following the song is mostly due to psychology and how we perceive music. One common usage takes advantage of the fact that the brain "fills in" sounds in the music that are "clearly" missing, creating the illusion that something is heard there, even though it doesn't occur in the music. For example, if there is a particular note in the music that is bland, adding ghost notes can trick the brain into thinking there's a flourish or embellishment where there isn't one.
Try to focus on the feel and flow of the chart rather than the literal technical usage of each note. Throughout the entire chart, the distinction between sync and ghost notes is a little blurred, but that blurred distinction against somewhat ambiguous percussive background sounds fills in a rhythmic groove and sets up the tone for the highlighted sections, allowing those embellishments to freely add color without feeling like they are misplaced.
In addition, it can be argued that the sounds of your own keyboard taps could be part of the music you are now listening to. The ghost notes could be, in a sense, adding percussive layers to the song that you are working with, effectively meaning you are drumming with your fingers.
There's a saying in jazz music: "There are no wrong notes in jazz." By adding context, you can make any "wrong notes" sound good. Ghost notes are similar in that respect. Ineffective usage of ghost notes can be mildly distracting or even unnoticed if it is a minor mistake, but is very obviously an error in more serious cases. If you are constructing a chart that seeks to be very organized and literal in following the music, ghost notes will be very pronounced and difficult to justify. Care must be taken when using these notes intentionally.
Notably, there are more abstract and avant-garde styles of designing charts where most all of the notes are ghost notes, and the appeal of such a chart is the abstract feel of the patterns themselves, rather than any of the notes' literal purposes. In these styles, the concept of "erroneous" ghost notes is almost functionally meaningless.