True, but then computers do not have tabs either. File folders have tabs, some books have tabs, soda cans have tabs (of a different kind), but not computers. Computers only have a tab metaphor.

The metaphor used in a browser with tabs, or a configuration screen with tabs, or an HTML page with tabs is consistent to the degree that each has a set of user interactable elements called tabs and each tab is associated with a set of widgets or content and that when a selected form of interaction (typically a mouse click or keyboard navigation) is performed on a tab the content or widgets of the previously active tab are removed from the screen and the content or widgets of the newly active tab are displayed.

That a tab is rendered by the OS, by an application, or by HTML/CSS does not negate the common metaphor they share, so if any are tabs they are all tabs.