If you added 1-2 inches everywhere on your body (or reasonable areas like quads, calves, biceps, triceps, chest, back) you'll definately see a difference.
People eat tons of calories simply so they can have enough fuel (better safe than sorry) for their body to grow. It's better to eat too much, than too little. Of course you can't get the EXACT amount of calories you need to grow without fat gain, but you can get close. So people who get fat are also packing on muscle underneath.
The reason they're back where they started afterwards is probably because they didn't diet down correctly. They probably did way too much cardio and didn't keep up with their meals, thus causing too much catabolism to occur and they lost most of their newly-added mass.