"The report followed a leak of military footage that showed apparently inexplicable happenings in the sky, while navy pilots testified that they had frequently had encounters with strange craft off the US coast."

I read it as, "We detected several times a military aircraft, that a country expected to be undetectable, flying over our territory, we send you the proof that such plane could have been knocked down; stop doing it" at same time they don't admit such other country violated the territory having to rise up a conflict.