Well, I'm not so sure there are necessarily 'rules' for weight loss. Obviously, if there are, "Don't eat fried foods" would probably be in the top five, and I also would have expected a gain, but it seems like your body is working for you. If you've been working out and eating right, your body has most likely become much more like a furnace, able to burn up the extra influx of carbs and fat. There is a theory of junk spiking, that you should eat a bunch of junky food like that every once in awhile while dieting to kind of shock your metabolism into kicking up the heat. If you return immediately to your eating plan and exercise, the damage is minimal or nonexistant, as it seems to be in your case here.
I say don't sweat it, leave it behind you, and keep on trucking.
you're doing a great job.