that is drastically over heated the melted scale on the handle indicates is was well over 22/2300 degf. 5160 isn't particularly sensitive to overheating, but it will get rapid grain growth at those temps and will crack and fail, especially if soaked for long periods. At several points in the clip it looks like the material is sparking, this is well over welding temp.  It is hard to tell in the speed up clip but it also appears that the material spends a good deal of time just sitting at high temps in the forge. that is not ideal. with simple carbon steels like 5160 it is better to het it hot  and work it as soon as it is back up to temp.