Draconian to say the least. That extent of pruning will cost you at least a year in the development of the tree. But that is just my humble opinion. Citrus can be pruned in almost any manner or shape that you like; it is your tree to do with as you like; but for me I would not be posting a video as "the way to do it", when very few would prune such a young tree so drastically.

Why would you prune such a small tree that way? Do you hate fruit?

During the first years, there is absolutely no need to cut a young citrus tree, since research has shown that any cut to a young tree reduces root growth. This is due to the equilibrium between the foliage and root system. A citrus tree is a biological unit. Cuts on a young tree, discourage canopy growth and delay trees coming into bearing. the only pruning on young trees should be to eliminate the central leader branch at about 30 inches . In some weak citrus varieties such as limes, satsuma, etc., it is not convenient to make any cuts at all. After a few years, DEPENDING on the speed of tree growth, climate and cultural practices, a very selective canopy thinning may be carried out. A two year old citrus tree should have been much taller than your tree was before you cut it. - Silica