The listed weapon lengths on the site measures the length of the weapon model itself, not the actual effective reach of the weapon in combat. The actual effective reach of the weapon is determined by the class of the weapon, its attack animations, and how it is actually being held by your character. Generally speaking, when comparing weapons from different classes with the same listed weapon lengths (ie a 100 length 2h, 100 length polearm, and 100 length 1h), the 2h will outreach the polearm on all attacks except for the polearm right swing (and maybe the overhead), while the polearm will outreach the 1h on all attacks except for maybe the 1h right swing.
As for how this specifically relates to your video, look at how the War Spear itself is gripped. Even if it is 150 weapon length, the fact that your character holds it near its middle means that its actual effective reach when swung is going to be far less than that. Add to this how all 2h swords are held near the end of their weapon models on top of having the best attack animations overall (the 2h thrust gives the greatest reach bonus in the game of any melee attack), and it's not really surprising that you were outreached there.
