Exams not being a good measure has nothing to do with learning styles.
If a learner is not oriented towards written or read communication, their exam results may not reflect a written test. If a learner has problems with their practical skills being observed in action, a practical test may not reflect their actual skills or understanding.
Being unable to communicate what you have learned is a serious disorder and not a learning style issue. Learning styles are about how you learn, not how you demonstrate what you learned.
But yes, people who are unable to write or read or very bad at writing have problems and tend to get extra support on written exams to make it fair for them, as the exam should test their knowledge and not their ability to write. For example they don't give blind people a zero just because they failed to read the exam.
It's absolutely a learning style issue if those teaching are not able to pick up on the issues with learning if the person being taught is unable to effectively communicate how they are struggling.
I spent years trying to explain to teachers why I did not understand some of the concepts they were telling me, and they would often tell me to just 'accept it' and move on. Bad teachers perhaps, but that's all part of the learning and others seemed to be fine... so that is a learning 'style'.
Your suggestion of 'serious disorder' is also misplaced.
Learning and expression of what is learned are part of the same learning process and it is entirely artificial to separate one of them to be part of learning style, and the other as not being part of it.
Virtually all learning is also learning how to express the subject being learnt.