You can't decide whether it's "obviously a button" in isolation. Depends entirely on how that particular element fits into the rest of the page.

The only exception I can think of is that it's obviously a button if it uses system controls.

Things that look real-world buttons or switches are more obviously a button in isolation than things that require a lot of context. Things can look "pressable" without context.

Those are quite obviously buttons. The difference is the design is flat versus the style in the post.

Those are a thousand times better than "buttons" that are just underlined text.

Or simply bold blue text.

Test test test test test.

I'm no UI pro but there's one thing I'm confident in saying through my experience and it's that you can't be certain something is intuitive until you've tried it on real people in a real scenario.

Your example button is fine with me but I feeling like it's the sort of thing that would confuse my mother. Acceptable depending on your app but I'm guessing that's Skype or similar and the 60+ market is probably important for them. But maybe I'm wrong, test test test.

I strongly disagree that it's obviously a button.

Lots of websites use that little pill shape for other things.

A button should announce that it is clickable, while the rest of the UI isn't. Just because something has a different background and shape doesn't tell me it's clickable.