I agree, S/V was romantic and cute - people were saying "Yah, finally", whereas, Jack and Katya was, as someone earlier put, "Huh" - nothing really to it, just shock!!
Because first she said he was sexy and then he was having that whole convo with Vaughn about coping with betrayal and handling things and he got upset about all his issues with Irina being paralleled in Lauren/Vaughn's relationship so he went to Katya's and was like 'just so you know, I can go through this on my own' or something like that and made out with her.