It does one update and draw per tick, with dt being the time since the last frame as measured by the high-resolution timer API where available (instead of Date.getTime() which does not have sub-millisecond precision). There is also no assumption that the display will be running at 60 FPS, since displays which run at different refresh rates exist.
The way I see it multiple updates per draw is just a good way to burn CPU time for little benefit. If there are fast moving objects you want to collision test more accurately or something like that, then a specific feature to handle that case is far more efficient than running the entire game's logic repeatedly.