Yup. Twice I have done 12 hours of pretty much solid walking, although some of it was pretty slow (fairly steep + around 11,500' and of course I had my pack) and my Fitbit says I haven't broken 50k. I gathered nothing, stopped only to eat or because I had to catch my breath (5000' of climb).

I was curious about the math for this so I found one of my high step count days. It was 40k steps with 34.6km ran/walked, so 60k steps would be around 47-48km, let's round up to 50km. A 5km/hour pace is actually more of a stroll (for me) so 10 hours would be the high end for me for walking 60k steps. I wouldn't be able to bring it down to 5 hours without getting into a jogging or slow run pace (10km/hour), though at the time I probably could've done that (I was running long distances regularly. So for me a 60k day suggests 7.5-10 hours of walking. I looked at some other high step count days (25-35k) days and they show similar numbers to that one.

I tried to do the math as well and I can't see how 60k steps on average works. From what I can see online your 2 steps per second is somewhat on the slow end but even at an ideal speed (apparently 180 steps per minute / 3 per second) you are still looking at 5.5 hours of running.

This seems achievable for someone very fit who wants to burn the weekend on an ultra long distance run but there is no way they are doing this daily.