Yes, you guessed right. The fans started it, and Misha now encourages it every chance he gets, in a joking sort of way.

There's a lot of face-stroking and such from both he and Jensen, and Misha once said that something (can't remember what) "warms the cockles of my heart. Words chosen carefully."

So Misha's behavior is nothing new, nor is him getting other people in on it. He even had a recent interview with Larry King where he said, entirely deadpan, that the actors have sex with each other on set.

Also, contrary to what some of the people say up there, I'm pretty sure you can lay claim to lead actor once you're a regular on the show.