How do you quickly sit down?

I've been trying to get the trophy for which you need to sit down and meditate wth another player for 20 secondes, but by the time my character sits down the other player gets impatient and leaves, probably assuming I've gone afk.

However, one of those players once or twice sat down almost immediately after he stopped moving, and after trying every button I still haven't figured out how he did it.

PS: One of those times, after maybe 5 seconds, that same person disappeared a little like sand in the wind. What the heck was that?