Just watched the replay and tested myself too.
It seems that Guard order works for gunships as impulse capacitor. The unit keeps getting more and more impulse, but for some reason its position reverts every frame, so effectively the unit just shivers in place. But the moment you cancel the guard order all impulse gets released and you can even throw Krow over whole map.
Only works for some gunships, presumably those with CanAttack=true.
Works for Krow, Blackdawn, Blastwing.
Doesn't work for Crane, Valkyrie, Vindicator.
Vindicator has CanAttack, but it seems to be flying too high to gain enough horizontal impulse.