Law enforcement sources tell TMZ ... authorities reviewed surveillance footage from last week's chaotic scene. They determined the group of bikers obeyed all traffic laws and didn't intentionally try to make it sound like there was an active shooter ... so, no reckless endangerment charges for causing the mass panic.

We're told surveillance video showed the bikers riding on 42nd Street when the group stopped at a red light. When the light turned green, they throttled up, and that's when a couple bikes backfired.

We're told footage shows only a handful of people initially ran for cover, before full-on panic set in. Understandable, given the uneasiness following the recent mass shootings.