Let's see if I can help.
You know how, for example, on MR, you have discussions with other people because of your common interest in fountain pens? Or how any two people / group of people can find some common ground over a topic, product, band, author? Like a club?
This is simply people finding some common ground over the ownership of a Jeep Wrangler, it's an extremely iconic vehicle, it's been built since '44 and started life as a military vehicle built by Willys–Overland Motors. There's kind of an association with people who dig on exploration, are a little more "free spirited", it has some unique design elements like the roof, doors are all removable.
The "ducking" originates from a bad experience an owner had, and in the moment, felt better just because of a silly little rubber duck they had in their Jeep. So the story circulated, and the mix of the "happy duck" and the general sort of Wrangler owner comradery (and kind of common life outlook of owners) got fused together, and Jeep owners started giving other owners a, "Hey, saw your Jeep, I have one too, here's a silly little rubber duck just to say hi, and I hope your day is going great!"