They aren't the same. Disinterested means not taking sides/being neutral.
So, Jane is not interested in football. She is uninterested in it, has no interest.
Sue supports Man U, so she enjoys seeing other teams play but doesn't mind who wins - she is a disinterested observer.
The meaning of 'has an interest' might be relevant (Philippa holds shares in Unilever so has an interest in seeing them do well).
Have just read loads of posts about ILs being disinterested In their dgch and it's made me go Aargh!
Phew. Thank you.