Music students spend a lot of time studying musical notation, terminology, and theory. Of course, many musicians don't read music while they perform, so this emphasis on reading is obviously not related to one's ability to play their instrument. Rather, it's about learning the language that musicians use to communicate, and that is an important part of music education that we shouldn't neglect.
However, some beginners aren't able to read music, or they aren't able to learn to do so using traditional methods. It is therefore necessary to allow them to adapt, whether that means learning entirely by ear or approaching notation differently.
Dyslexia is not related to vision or intelligence. It is a learning disability related to language and affects the development of speaking, reading, writing, and spelling skills. Because musical notation is the written language musicians use to communicate and includes its own terminology, it can be confusing for someone who is dyslexic. Often, a music teacher isn't qualified to help with the challenges dyslexia presents. Whatever approach they typically use in teaching their other students might be ineffective for a student with dyslexia.
There is another lesser-known condition, dysmusia, which specifically affects a person's ability to read and interpret musical notation. This is different from dyslexia, although it is possible to have both learning disabilities. However, there might be less motivation to address dysmusia because for most people, the ability to read music isn't necessary, whereas literacy is. Someone with normal vision and intelligence who always performed well in school might never understand why reading music is difficult for them when it seems like no one else struggles with it like they do.
Regardless of the difference in symptoms between dyslexia and dysmusia, the results are similar. The student struggles to learn to the language musicians use to communicate, and this in turn makes it difficult to understand basic concepts like rhythm and pitch if these concepts are primarily presented in written form. Someone with undiagnosed dyslexia or dysmusia might believe they lack "talent" and need to quit music - and it might not be their first "failed" activity. The damage to a person's self-esteem from repeatedly "failing" isn't healthy. It doesn't help matters if a parent or teacher labels a student as "untalented" instead of providing accommodations or doesn't view dysmusia as a condition that requires treatment.
Whether a student needs a different approach to learning how to read music or perhaps would find it easier to play entirely by ear, there is nothing "wrong" with such accommodations. They don't make the student incapable, and a teacher isn't failing a student by not insisting they do things the traditional way.