I think the distance was probably accurate, but it was a somewhat windy day so Mathathi may have had some tailwind advantage. He was also chasing on his stage, not leading, so there may be some advantage there as well.
Still, he had the old stage record of 26:19 too, set in '07. Since then he has gotten a WC 10000 m medal, broken 27 on the track and most recently broken 45 for 10 miles, so it doesn't seem completely impossible.
The next fastest guy, Samuel Ndungu, ran 26:24, also pretty smokin'. 3rd and 4th on the stage were in the 27:20's.
Complete results:
http://www.meigi-ekiden.com/2010seiseki.pdf