Are you sure that isn't just the Midgar stage materia effect. Bahamut ZERO is still going off while that happens. Let's see
Oh, wow this is actually an inanely good discovery.
Still 1, Blade Beam going off towards Pit
Still 2, Blade Beam hits Pit, a circle effect is seen around Cloud
Still 3, Pit is hit up and caught in Bahamut's attack, the circle effect stronger
Still 4, The last shot before it becomes far to difficult to tell what's going on. Unsure where his sword position is now, however there is a VERY distinct blue glow effect around Cloud, while the Red glow seems to have been fading.
And for comparison sake, the Limit Charging special
There's no mistaking it, that's the same glow and ground effect imo. Seems Cloud builds limit by HITTING with his Normal Limit Breaks (as it only charged up once Pit was hit by Blade Beam).