I've read many accounts on the Mongols and they are all consistent in maintaining that the bows were powerful. At the time of Genghis Khan, the tradition of shooting composite bows had existed for hundreds of years. This leads me to believe that the quality of the average Mongol bow was very high, and that the test results are not surprising.
If the same arrow was shot out of both bows, then the speed of the arrow was greater when shot out of the Mongol bow. It's that simple. If the arrows were different, then there is no telling what the cause was for the greater penetration... and the test is meaningless without complete data on both the bows and the arrows.
As far as Comanches vs Mongols, the side with the greatest levels of morale, technology, and training would win. In this case, the Mongols would have the upper hand. JMHO