50 miles a day? That's truckin. Can a body take that much stress? Regardless of how conditioned someone is.
For a week, an ultramarathoner and cross-country runner can manage it. The current Appalachian Trail supported record of 47 days, 13 hours and 31 minutes means that ultrarunner averaged 46 miles per day for over a month and a half.
To pull off a one-week hike on the Pinhoti would also mean an average of 46 miles per day, sustained for just one week. Add to this fact that there is much less climbing on the PT versus the AT, as well as 85 miles are on smooth road, and it's certainly doable for a certain caliber of athlete. It's still a very impressive feat should they pull it off, but quite doable compared to other such long-distance runs.