So I was playing a game of league earlier and the enemy adc picked up a quadra kill in a teamfight. During this particular teamfight I was still coming for base and as a result, I showed up late to the fight. But as I arrived, the enemy adc picked up the quadra and turned to me (I had full health as I had just come from base), and I killed him with one auto attack.

Immediately after, pretty much everyone in the game (both teams) started yelling at me and calling me rude and a b*tch because I didn't give him the penta.

I thought the definition of a penta was when "A player manages to kill all five members of the other team in one team fight" and not "A player kills four enemies on the enemy team and then gets a free (full health) kill from the fifth player.)

What happened to actually earning a penta kill?