I don't count as someone who knows anything about music, but I agree with your assessment. Though I find the bit about MIDI files surprising, seeing as MIDI files and chiptunes don't have the same sound (to the extent that MIDI files have a consistent sound). I'm not sure how much this says anything seeing as going by the linked articles there seem to be a number of people who would agree with this.

Explanation number two is interesting. I had considered #3 to be the obvious explanation and hadn't really considered any others. Thanks for pointing that out. It seems easier to test than explanation #3.