I mean, in the time he takes to say "No but we can take a picture" he could have said "hello Kim and Tori" like she asked him, in fewer words and time too....
I'm not one for bothering Celebs, they should their own private time, but you got to realize with fame that's what it comes with. People enjoy your work and they just want a way to capture meeting you, be it an autograph, picture, etc, just a keepsake so they can show people in the future "hey I met x back in the day" or show off to their friends. You can be humble about it, oblige, even if you don't have the time you can say sorry and go your way instead and most people will understand.
Really not a reason he had to say no to simply saying hi to Kim and Tori in this instance, especially because it would have been shorter to do then complain and ask to take a pic instead.