Bipolar disorder involves you cycling between depressed to hypomanic/manic and sometimes mixed states which is depression with the sped up quality of mania, when you're having mood episodes. Hypomania is a lite version of mania, so to speak. Mania can involve destructive behavior to oneself such as gambling, running up credit card bills when you have no money, hypersexuality, decreased need for sleep, racing thoughts you can't keep up with, pressure to talk, rapid talking, impulsiveness, euphoria, gradiosity, etc. When a person has a manic state it's usually pretty obvious something is going on with them and usually can end up with a hospitalization if the person is around people who are educated in these matters.
There would be a big difference because if a person has depression then their mood swings would vary from depressed to stable (technically euthymic). If a person has any form of bipolar then their mood swings would vary from depressed to stable to manic and there are combinations in between such as mixed states. All of this is clinically complex and should be discussed with a psychiatrist but keep a mood tracker and then print out the results for them. Then if they notice any mood swings that appear to be part of bipolar depression (where depression is the general concern but there are episodes of mania as well) they could update your diagnosis and treatment within their discretion.