some adults that I know have been diagnosed with this because they have temper tantrums\ uncontrollable bursts of anger\rage/ these outbursts of rage happens at least 3 times a week, self harm and do not have the basic bipolar problems of mania\manic symptoms. though this diagnosis is for children some adults do score on tests as having this disorder.

my suggestion is talk with the treatment provider that diagnosed you with this. they will be able to explain to you how and why you fit this diagnosis despite the fact that you are not a child. it may just be that the tests place you in that because you "better fit" this diagnosis vs others and having this label gets you the right treatment options for your problems.