Does hypotonia and neurological disorder always goes together?

No: They do often go together, but not always. There are several conditions that involve muscular tissue or muscular inflammation that can affect muscle tone. There are also some diseases, such as myasthenia gravis, that affect the neuro-muscular junction. Sort of a neurological disorder. Often the pattern of hypotonia, e.g. Which muscles are weak, is important to tell the difference.

Not necessarily. : Though the underlying cause of hypotonia is undoubtedly neurological, it is not always associated with other neurological problems. Hypotonia can be part of neurological syndromes, but can also be an isolated finding with no identifiable cause.