In the linked video around 1:07, you can see that they already have vision on the tanks when the first one rotates to fire. This could be the result of a cheat,

In the linked video around 1:07, you can see that they already have vision on the tanks when the first one rotates to fire. This could be the result of a cheat, but SC2 does include NPC watchtower buildings that can be captured to grant vision over a large area of the map (you could also send flyers to scout). From there it is (or at least can) 'just' ridiculously fast and precise angle-tracking and micro, so this is a situational tactic at worst.