Interesting spike in backcountry camping in the Great Smoky Mountains relatively early in the season (starting in March). Probably thru-hikers on the Applachian Trail, hiking northbound?
It's also the nicest time to hike in that area, i.m.o. Thru hikers probably do contribute to the spike, but I'd bet a lot of it is just that April and May are the best weather.
I hiked the backcountry there two spring breaks during college. That was 20 years ago, but I don't really recall it being crowded. Beautiful time of year, but a little scary when I had to forge a river of snowmelt.
