I was battling a random person and this is what happened:
It was down to our last Pokémon, which had around 20 HP left each. His Magmortar was holding a Life Orb. He did Thunderbolt to me, and he killed my Jellicent, and afterwards, he died from the damage the Life Orb causes.
AND THEN THE GAME TOLD I HAD LOST. Why?! He both fell down!! It's supposed to be a tie!! It's not fair!! I thought that maybe he also got the message that he lost, so I wanted to know. Can someone tell me why did I lose if both Pokémon fainted at the same time?!