“running gait”
That implies that both feet were off the ground at some point in each stride. I wonder if it would have been more efficient for it just to walk. 3 miles in 53 minutes is not blazingly fast.
The video shows humans with cameras walking behind the robot filming. At some point it was a fast walk.
My best 5K time ever was was in the high 16s (in my late 30s) and I was no star, striving for adequate and an age-group medal. At the Monday evening races we used to run around a small lake every summer, the winner usually came in a little over or under 15:00. Even now I could walk it a lot quicker than the robot ran! But the arthritic knee would make me pay the price next day.