What Scott did was set the fastest known time on the trail, bottom to top. When Jennifer Davis set the record in 2011, she did it top to bottom. ..the ultra running blog-fights about which way is harder are pretty awesome, trust me.
There are records for through-hikers, that carry their tents, sleeping bags, and food with them. . . .They get water and supplies as they go. Those records exist somewhere. You are correct though, he did not set out in Georgia carrying four hundred and fifty gallons of water.