Been quite a while since I flew the 412, but without the charts in front of me and with Max gross around 11 700 those numbers look reasonable to me. An engine failure with that kind of DA could very likely result in an instant descent rate, with the least descent rate likely at around 70 kts and increasing descent rates as you get slower or faster than that.
Assuming the pilot didn't pull collective hard enough to fry the remaining engine and/or droop the rotor to avoid terrain. Sometimes we work in ugly places and there just isn't enough sky under you.