Known: {V0, V3}; Frontier: { V1, V2, V4, V5}; Other: { V6 }
The distances for the known vertices are correct.
But the distances for the frontier vertices should be updated.
Why? Because, there may now be a shorter path that goes through the new known vertex V3.
The new known vertex V3 is adjacent to frontier vertices V2, V4, and V5.
Only the distances to these adjacent vertices V2, V4 and V5 may require updating.