Obviously it was because MURPHY H4X!
Okay, well on a serious note maybe you hit a lag spike and didn't see everything? I don't know. Also hate can be a fickle thing, it ebbs and flows easily. Who knows what caused you to get hate, it could have been a number of things. I wasn't there to see what happened to give you any concrete answers and your analysis isn't very descriptive. I've had a few experiences with Murphy, on my other char I duo'd him with a RDM 75. Then to help some people I've been a few times on my BRD.
Murphy's drain is hardcore, i've seen it pwn a Paladin 75 before, but i've also seen a monk tank him.
It's likely your friend got cursed while you went down and was easily done in by the Water III. Though I can't say it like it did happen, thats possibly the most likely scenario. To be honest I don't really know what to tell you, other then "that sucks."