TV coverage of replays

just saw a major example of this on SNF
Seattle QB was getting stacked - ball seemed to slip out of his hands before arm coming forward (he was facing sideways as well)
ball hits off defenders arm and goes forward maybe 5 yards
Collinsworth was quick to say incomplete - they hustled whichever rules analyst sock puppet works SNF and he was quick to agree with CC - they go to commercial for the challenge (after showing another angle that was nowhere close to conclusive
and they come back from break and say challenge was denied

i'm like 72% sure it was a fumble