IMO, He is striding but it appears without much intent. He needs to drive forward with his legs and core, leading more with his hips. He appears to have somewhat of a short stride, which can be contributing to his lack of drive to the plate. There is a great drill that helps get the hips going, it's called the Hershiser dill and can be found on You Tube,
Arm action appears to be ok, I would like to see him get more hip shoulder separation by staying closed with his shoulders a bit longer. Also he can start working to get more external rotation in his throwing arm.