Take this graph, in this if we apply topological ordering, then 0 can't come before 4 or 5, BUT if we apply DFS 0 can come before them. What i mean is if we start topological ordering with vertex 5 then one of many order will be, 5,4,0,2,3,1
But if we apply DFS with 5 as start vertex then one of order may be 5,0,2,3,1,4
So, for this graph they are not same, may be for other graph it will be same.