Potion effects arent only in one match for example if there was a beacon in one fight and 2 other people queued the same map they would get the effects too, what happened is someone splashed poison when they queued debuff and you queued nodebuff you just both happened to queue the same arena.
Staff in v somehow got poison pot. Or another match between two players which would be "debuff". One threw the pot and it glitched into your match. Imma have to say bug as staff wouldnt do this even if they could.