Well, I don't really remember if the sceners in Sweden called it "chip music" when those cracktros with SidMON music etc first came. We might have called it SID music, because PlaySID had just been released on Amiga.
What's meant by the term I guess, is that on C-64 you could load a stack of parameters and start the sound, and the chip would play it "on its own". This is a bit of a simplification of how song players work, I know. But of course no chip can play a whole song on its own. But apart from having a "software sequencer" to run the "synthesizer" chip, non-chiptune players also had software snippets to run ADSR or similar sound transformations on sampled instruments.
On Amiga, of course there are only samples and software to transform them, so the distinction is harder to make. Maybe if it has mostly simple short waveform samples, and there is a proper instrument editor where you shape the synth sound of the instrument, it's a chiptune tracker?
I wouldn't say that a protracker tune that has 14 samples and 1 lead instrument as a triangle wave using commands to synthesize it is a chiptune.
But maybe the fuzzy definition is okay. "If it comes from a music program which has a synth-instrument editor".
That seems to be the general thinking, and you're aware of this too. The origin of the term could have something to do with the above guesstimate, or someone else will enlighten us