Said it before, will say it again. It was a bot.
The OP said he didn't run in and use it to telegraph his moves in advance and the fight was literally upclose the entire time and he didn't just spam it every CD. He also played like crap in all regards except his clairvoyance with the HoJ which BoTs can actually check for thanks to the delay between when the move is announced and when it hits (which even does that for instant cast attacks) which gives a bot enough time to react and counter it with relative success depending on latency which is why the success rate wasn't a full on 100%.
Don't believe me, check your combat log with time stamps, you will see a delay of a fraction of a second between when it is cast and when it hits which is more than enough for the bot to respond.