Zombie Nunu random kill?

So one day while on the rift I find myself not having the best of games. I was playing as ADC while my friend was playing Poppy. So while trying to push in top lane a little bit I find myself in a sort of a pickle, near the enemy tier 2 tower I find the enemy Lux staring me down as I approach. With nothing more than her E stopping me in my tracks I find myself to be backing off. However not a second later I see a very familiar face approach my person with evil intent, so as one would do I back off. However as I back off I see the enemy Nunu disappear within the fog of war. Without a moment notice I find my screen gone grey while me and my minions are all covered in green goo. Now my friend said "Possibly the Nunu flashed ulted beside you to kill you?" I said that was impossible considering how far i was from the edge of the jungles wall. I'm not sure if this has happened to someone else but damage can explain how I died but how the damage got to me. If anyone has experienced this then please comment back ASAP. Thank you to all who see this.