Wow that's an awesome rainbow! Somebody told me once they caught a 7lber near Trout Creek years ago but never believed them, maybe now I do lol.
The limit is any combination of browns and rainbows, not 5 each.
The upper Neversink is privately stocked with rainbows and some guys have caught them in the reservoir, DEC has even caught them in surveys there. Since water from Neversink is diverted down to Rondout anything that swims there could end up in Rondout, hence the occasional LLS that is caught in Rondout.