I can’t believe it took me so long to realise this. Aristotelians sometimes (read: often) use the word “motion” to refer to change of any kind. Thus it is much broader than how we might use the word today. It’s certainly broader than mere change in location, but even we use it in a broader sense that.
But why? Why would you call change, in general, motion? Good question.
One of the questions Aristotle had to grapple with (and which we tend to ignore these days), is how change is possible and what it is. He realised that any instance of change is the actualisation of a potential. When a hot cup of coffee gets cold, for example, what is happening is that the cup’s potential for the being cold is actualised by the coldness in the surrounding air (say). When I pick the cup off the ground and place it on the desk, I am actualising the cup’s potential to be a meter above the ground (say).
So all change involves the actualisation of potentials. But does every actualisation of a potential involve change? No.
Go back to the cup sitting on the desk. Say it’s been sitting on the desk for a while now. Its location isn’t changing, but the desk continues to actualise its potential to be a meter above the ground. (If this potential weren’t being actualised, then the cup wouldn’t be a meter above the ground in the first place!) But this actualisation of the cup’s potential clearly isn’t an instance of change.
So there are some actualisations of potentials that are change, and some which aren’t. What separates the one case from the other? Surely it’s that change involves the movement from potential to actual. That is, it’s not merely that some potential is being actualised, but also that that potential wasn’t being actualised before. So, to use fancy genus-species language, the genus of change is the actualisation of a potential, and the specific difference is by movement from potential to actual.
As a side note, since efficient causation just is the actualisation of a potential this specific difference helps us distinguish between something like state causation versus something like event causation, as these terms are used in modern parlance. (I say “something like” because the Aristotelian thinks that (1) substances are the fundamental kinds of causes, not states/events, and (2) whereas typical construals of state/event causation involve one state/event causing another, Aristotelians typically understand cause and effect as two aspects of the same state/event.)