Sorry about your unfortunate experience. Having been born and raised in NYC, and knowing that part well due to working a couple Summers in Brooklyn... I can only add that you wandered into a less than desirable section of Coney Island. West of your location is Sea Gate, a gated old community guarded by NYPD no less. Those residents have the clout and money to fence out the ghetto-ed surroundings. If you wish to bike along the beach, I recommend the Sheepshead Bay portion at the eastern end (Manhattan Beach, K.C.C.). If I were you, I'd stay on the gateway along the Belt Pkwy overlooking the harbor and the Verrazano Bridge. Much safer.

During my time in the city back in the early 90s, I was witness to two shooting incidents, both in Manhattan. I can only offer that NYC has improved since I was a kid in the 70s. There will always be such incidents, but you must be aware of your surroundings and know the trouble spots. It'll keep you out of trouble.