You are correct, there is some overlap between vision and strategy. There is no line per se, but strategy itself is such a broad term that can be applied in many, many places.

A strategy is a hypothesis - or as Roger Martin states -- a series of where to play, how to win decisions to achieve an objective.

I do mention that the stepping stones "overlap a bit with high-level strategy", and that's fine The Tesla master plan that lays out the steps they would take on their path to creating an affordable car is a very high level strategy. i.e. they believed that those steps would be a path to achieving their goal.

These concepts are related and flow from one to the next so it's important not to assume there are always hard lines that can be drawn between them, despite what my diagram or other diagrams might imply.