Quoting the video maker:
In this video, I put a tank hidden near a bush in the training room. I then went after it with another tank and rammed it. the video was recorded live, it is not a replay (a replay displays the FPS differently). At no point did the enemy tank become visible or spotted, I rammed it, and for a few seconds I was pushing around an invisible tank. this bug was introduced in the 9.15.1 patch.