I imagine that when you posted, you were figuring, "Oh, I don't know aikido, but I remember this cool wrist thing. I'll ask the aikido people what 'the wrist thing' is, they will recognize it, tell me what it is, and I'll be able to use it and move on." Sorry, but I don't think that's going to work out for you.
First of all, the aikido practioner that you met could have come from any number of mainstream or more "progressive" schools, where they could have studied an array of variations that most aikido practioners might or might not recognize.
Second, there's a lot of different "wrist things" that will get you on the ground. Personally, from your description (and personal experience with what gets good appreciation as a party trick), I'm envisioning nikkyo. This is [other aikidoka: this is my own explanation; you may or may not explain it similarly] where the outside non-thumb side of the hand is grasped and rotated sort of inwards in a corkscrew twist, while the wrist is held to provide tension.
Third, I'm again sorry, but I don't see that just knowing a name is going to add much to your work. "He did nikkyo on the Bad Guy, causing the Bad Guy collapsed like a house of cards. He then... " So what do I suggest? I suggest that you take up aikido. Not too likely, but I thought it was worth a shot.