3 vehicle collision: not at fault

[iFly55]

i really don't know if i was involved or not, it all happened really fast

we came to an intersection the vehicles infront of me braked hard, my brakes (vehicle A) locked up.. i swerved away from vehicle B into a left turning lane

i heard a crash, and i saw vehicle B crash into vehicle C, vehicle C may have also went into another vehicle D... who advised he and his vehicle were okay, and left vehicle C his business card and left the scene

vehicle B had moderate damage to front bumper and vehicle C had minimal damage to back bumper

because of our close proximity i didn't know whether i was involved or not, my plastic front-license plate cover appeared to be cracked (not sure if from before), however no damage to rear bumper of vehicle B

passenger in vehicle B advised she had a heart murmour and had trouble breathing, and no one else had a cellphone... so i stayed and called 911 and 30s later we had 2 ambulance, 1 firetruck and 2 police cars surround the scene

i was told to wait at a nearby parking-lot, to allow traffic to flow through the left turning lane

there were two occupants in both B & C, they both had their cars towed and it looks like they all went on the ambulance

when i asked the police how passenger B was doing, they advised everyone was okay, and that there were barely any damage to warrant any injuries

i wasn't given any tickets, or a copy of the accident report, just given the accident report number and officer name & badge#, written on my insurance slip

the officer, i quote advised me, "i was not at fault"

what does this mean? and what should i do?