The event documentation it says that item_remove is

Invoked when an item is deselected.

Explanation:

While from what I know the selection concept is about having a subset of (one or more) items in the state active.
So I understand "deselected" as not having any currently active item (e.g. when clicking outside of an item).
The item_remove looks like triggered when an item is removed (via remove-button plugin or backspace/canc).

Reasoning on terminology

It might be that the terminology overlaps because of having a Selectized control that allows to "select" values from a list, but where these selected items can be further "selected"/"activated" as a subset of the actual value selection.
The "activated" items will allow to remove a subset of the selected values altogether, while all the "selected" items will anyway be submitted as form-data value.

Question

Did I understood correctly or the documentation is actually right in using that terminology?