The secret is fairly easy to explain, and I'm surprised it hasn't been discussed yet as it's so ancient that it's hardly a secret anymore in the magic community.
At 2:36 in the video, you can see the utilization of the famous "ghost bench" illusion. While the bench the couple is sitting on may seem innocent, we all know that's not the case. I realize I don't need to go into too much detail here regarding the prop's workings, but it IS an old premise and may need some clarification, so I'll be concise but brief.
Each of the slats on the bench is hollow and contains a full deck of cards within the faked wooden planks. As long as the performer sits on the right (meaning "not left") side of the bench and places the first card selection down on any of the 9 slats (there are always 9 due to the "rule of three"), he (or she) can feel confident that the prop will do the rest of the work so the performer may concentrate purely on presentation...as does our man here.
From there, the rest is mechanical. As the volunteer is choosing her card, the magician has his toes carefully placed on two buttons built into the cement base below the bench. Once the spectator's card is revealed, he uses his feet to transmit Morse Code to the secret assistant hidden below the bench and base in a carefully disguised bunker built weeks before.
Don't worry. The hidden, buried assistant has had plenty of stored food and beverages to stay alert.
The assistant then decodes the message, and keystrokes the now-known spectator's selection into a complex keyboard-clockwork apparatus within the bunker that is connected by system of hermetically sealed air-operated pistons connected to the hollow bench slats above. The correct bench slat is discerned by the assistant through a steam operated scale determining which portion of the bench is being sat upon, and said assistant is able to dislodge the appropriate card hidden within the proper slat to serve - through a mini-conveyor belt and slot in the bench's surface - the correct card to the magician, who quickly switches it for the original card already setting upon the bench in front of our innocent spectator. This is all done under cover of "reality simulator" silk (of course designed by Robert-Houdin in 1869) casually, and invisibly, tossed down by the magician over the original card on the bench, that disguised the mechanical robot arm coming up through the slit in the hollow bench slat to deliver the "prediction."
It's so simple really. As all great magic is.
Sorry dangalhardo...just trying to have a little fun. It is a really good trick that you shared, but we don't discuss secrets at this level. Yet, if you keep hanging around here and contribute...and we hope you do...you'll find a lot of people willing to show you down the rabbit hole. And the hole runs very deep. Welcome. And enjoy...