Ghost may have been full the first time you wieghed him and he may have just pooped when you weighed him most recently.
As long as he's active, is eating, feels strong when he jumps and climbs and looks good, I wouldn't worry too much. They go through growth spurts, remember. Sometimes they'll grow like weeds, then just stop for a while, then fatten up, and BAM! they grow again.
If you're really worried, you can have a fecal done to rule out parasties.
Just get the freshest sample you can, put it in a zip-lock baggie and refrigerate it. Put the date on the baggie if you can't get it straight to the vet. Explain the situation, you probably won't even have to bring him in, so it shouldn't cost as much doing it that way.
Help! Crested Geckos! 0.1.Leachie, 2.1.1 Gargs, 1.0 Chahoua, 2.1. Blue Tongue Skinks, 1.1. White Lined Geckos, 1.3. African Fat Tails, 2.2.0 Tokay Geckos, 1.0. Giant Day Gecko, 2 tarantulas