Twitter admits to limiting visibility of posts.
So the dispute becomes a spectrum/threshold question. Most people would say that if 10% of the people who would normally see your posts get to see them, that's pretty shadowban-y. And most people would agree that if 90% get to see your posts, that's more like "limiting visibility" than shadowbanning.
The key questions are: (1) to what extent was visibility reduced, and (2) at what threshold should we consider "limiting visibility" to be tantamount to a shadowban?
There are also indirect effects to consider: if your posts are shown to only 60% of the people of a normal post, then you will get fewer RTs and fewer new followers in the long run. So consistent "visibility limitation" has a compounding effect that could substantially slow your account growth and reach over time.