Agreed, colic is not a disease unto itself, it is only a symptom.
As a fever is not an illness unto itself, it is only a warning signal of an illness. Many medical conditions cause fever, many medical conditions cause colic...
I was defined on hospital records as having colic when my gall bladder had filled up with gall stones and caused me severe pain.
BTW....colic is defined in the dictionary as severe abdominal pain. A tummy ache....which can be caused by a number of things....some transient, some not.