Often in the media when non-binary people are represented they are shown as white and androgynous. While some non-binary people may look like this, this should not be considered the norm or the standard.
Nor does a non-binary identity necessarily mean that the person identifies as genderless. Although they can.
How each non-binary person sees and understands themselves is unique and cannot be assumed. The one thing that can be assumed is that they do not their identity as simply falling into the dichotomy of male or female.
If you have the type of relationship in which it is appropriate to ask about this type of personal information, then ask them how they see and understand themselves.
Otherwise, it is not your business and you don’t need to know. And they don’t owe you an explanation.