I've been seeing cheek kiss and handshake greetings more often since the Pets EP dropped, even though I don't own it. And they are not limited to townies. Sims from the household I'm playing (generally the female adults) will surprise me by waving at an NPC, say Jasminder, on the street, (without being "told" to), and then initiating a conversation following a "cheek kiss" greeting. The men will do the same and shake hands or sometimes give each other a toned down "bro hug."
I am loving the autonomy of these interactions and have noticed them happening in the "newer" cities of Windenburg, San Myshuno, and, yes, even Forgotten Hollow. And it's not limited to player controlled Sims and NPCs. I have also seen NPCs and Townies greet each other in similar fashion. I hope this is not a glitch or bug, because these minor little touches breathe life into background Sims that are usually little more than Zombies.