I’ve just seen that in Blender 2.90 you can select a “Mode for calculating rotation channel values” which is set to “Auto Euler” per default:

Since the “Bone Rotation” in “Pose Mode” is set to “Quaternion” per default, one might suppose that this could be the explanation for the discrepancy described above. Blender 2.67, which is used by Kent in the video, doesn’t offer that “Mode Selection”.