What's the story behind it? Where did it come from?

Assuming a "virus" Fizzer made and whoever defeat him spread it around?

I learned it may have been HHH who was patient zero.

So why him?

The viral achievement was introduced with a bunch (or, at the time all) achievements around Juli 2013(???). It was Heyheuhei who got the achievement first, from there it spread around the community. [1]
In https://www.warlight.net/MultiPlayer?TournamentID=5455 was the first time HHH lost, so at the end of the tourney 4 players had the Viral Achievement [2].
I'm not sure why HHH was chosen, but someone else should know that...

Sources:
[1] https://www.warzone.com/Forum/6460-viral-achievement
[2] https://www.warzone.com/Forum/80481-first-viral-achivement

Edited 9/21/2020 07:19:48

This should help my curiosity. I'll look into the links.

Wow, mate, I told you don't swallow all pills at once. Now you are overpilled.

who did suggested the viral achievement and what version was it added?