Hmmm,
First, when I click on the three-bars button in the upper left corner, it indicates "feet". That window indicates one can purchase the map in meters, fathoms or feet. Yes, changing the units drop-down box and clicking "Apply" doesn't change the numbers on the map.
Second, when I scroll the linked map over to New Zealand (or England/France), I note near-shore contours of "98.4" and "164". These, if in feet, convert to 30 m and 50 m. But who's to say one part of the world map uses the same scale as another? (But it is suggestive!) Some detailed areas of the map show no contours; around Elephant Island there are contours in even thousands, and one at "200". Around Germany I identified a contour at "65.6" which, if in feet, converts to 20 m.
Scrolling on what gives that paper, Baking? (Scrolling the map down takes me to mid-Antarctica [and no further], and scrolling left takes me around the world until I'm dizzy.)