Why did Gabriel tell his brother that the NOMAC's were down in Moment of Betrayal?
Because when the NOMACS are down, he could practice his gift of music. He's also basically informing his brother that he is meeting Nafaryus as arranged by Faythe, which was in the lyrics to Road to Revolution:
"He only sees what he desires to see
It took a while but finally he agreed
Though everything did not turn out as planned
If life's a risk
It's worth a chance
I know where there is faith
There's always hope
They'll meet beneath the stars at Heaven's Cove
The ghosts of yesterday
Once filled the lavish stage
Taking our first step down a new road"