I am a german native speaker. The is indeed no difference. So the context is important. But in informal speech you often say "is' " instead of "isT". Er is' 'ne Orange. (=er ist eine Orange.) = He is an orange. Er isst 'ne Orange. = He eats an orange. With enough practice you might hear this difference.
There really isn't much more to say. Here's all I can really find on the topic.
That's not correct. The singular is "eine Orange".
Er isst eine Orange.