The issue is the same either way. The pointer event is not just restricted to the slider, but is shared up and down the document tree. You can see the same thing if you put a button on an expandable f7-card. When you click the button, the card responds (in fact, my example of getting two oh actions out of a single button actually relies on this particular behavior). This isn’t something specific to OH or MainUI, is standard javascript event handling.
There are ways to prevent the event from “bubbling” like this but you don’t have access to them via the widget system; that has to happen as the level of the component’s javascript (in this case, I would think the f7 library, not just the the oh-slider definition).
These are, for the foreseeable future, probably incompatible functions and you’re going to have to choose between the slider and the swipe-to-close.