Still wondering why triforce has random movement speed attached to it

Okay hear me out here

If you don't account passives or actives from an item, AN ITEM WILL ALWAYS GET ITS STATS FROM ITS PARTS and normally when you reach the final tier items the stats might increase slightly so I'm simply wondering

why Triforce just so happens to have 5% move speed even though NON of its parts actually have move speed attached to it?(not counting phage)