Is the top-down sorting of videos in a VOD Channel responsible for the left-right sorting within Media Groups displayed on ConnectedTV Apps?

Yes, the top-down sorting of videos in a VOD Channel, assigned to the same Media Group, equals the left-right sorting, meaning, in order to have videos show up sorted left to right within rows of Media Groups (Series) on TV Apps, they have to be sorted top-to-bottom (from lowest to highest number) within the respective VOD Channel.