Addon game version higher than WoW game version

[Spekky13]

Hello community,

Could anyone tell me how this is possible? I saw someone streaming from Warmane on Twitch & was interested in his addon. Although the only version I could find was above game version 5.x.x Obviously this didn't work, but why is his working? The addons name itself is "BLT Raid Cooldowns" or "Blood Legion Cooldown" Any ideas? See link below. Thank you in advance.

[Nerosempire]

https://github.com/freix1/BLT_WotLK

[Spekky13]

Thank you kind sir!