He used a card to steal control of the Revival Jam which made Slifer auto-attack it. When Slifer killed it, Strings had to draw cards. The Jam revived, causing Slifer to attack it, and Strings had to draw more cards. It looped until Strings lost due to his deck being out.
And this combo doesn't actually work in the real game. Revival Jam only revives if you pay a thousand life points and only does so on your next turn. On the other hand, I don't think Yugi's counter would work either because Card of Safe Return lets you draw a card when something is summoned from your graveyard. I would assume if you steal the Jam, it goes to your graveyard.
Did this duel in the anime precede the real life cards?
this was back when the anime was still playing fast and loose with the rules. a lot of cards (like the God Cards) had different effects in the anime, even when they started following the real rules more. ---