As told by the guy who did it on YouTube:
In this video I mentioned the #1 biggest METAL hits of each year of 1968 to 2017. From this video you will get known about the songs which have dominated over all metal track released in a specific year. I didn't make the list based on personal opinion. The list is made after researching on music charts, award and nomination choices and many other tabloids and magazines. So consideration of the critics receptions and accolades of the songs made these songs listed. The list is not only created on popularity basis . That's why some popular song will be seemed missing and some unusual song will seem invaded. Though multiple track became successful in some year but only one track is picked for a year. On contrary some year has no metal hit. So in all the way most appropriate track has been selected in compare.
The poor guy had a shit storm because he put Charles Manson's all time favorite song: The Beattles "Helter Skelter" in it. Nonetheless, it was probably the closest thing to Metal in 1968.