I am not sure if they rate rock samples as "ppb" as they are rocks not soil but 31.4 grams per ton is massive. And heres the important thing about it. The soil sample containted close to 6 g/t, so they took the rock sample from underneath the same area that they got the 6 g/t reading from and found 31.4 grames per ton in the rock.
With this type of deposit the deeper you go the more gold you should find until you reach a certain level. The fact that they found roughly 6 times more gold in the rock right under the soil with the highest readings is very impressive and would strongly indicate that there is much more under that in the other rock layers and could go down 100s of meeters.