What's this statistics-looking icon on my TouchBar?
Solution 1:
Are you watching a video in Safari? That slider is telling you that you're watching a video in the app displayed in the icon, scrubbing on that slider scrub the video you're playing. Or if you're not watching a video, it might just be a bug. Try refreshing the Control Strip by going into activity monitor and find the process "Control Strip" and quit that process(it won't do any harm, your touch bar will blink once).
P.S. As for taking screenshot of the touch bar you need 10.12.2 beta.