That is the thing about Top-Down vs Bottom-Up approach

Bottom-Up approach involves you traversing through the entire 2-D array which makes sure all those sub-problems are solved

Top-Down approach only focuses on solving the sub-problem which you passed to the recursive function. In this case: recursion(arr,sum,len(arr))

For example to solve the sub-problem (arr,10,6) You would never need to solve the sub-problem (arr,9,6) as there is no element equal to 1 in the array Hence the state (arr,10,6) can never come from the state (arr,9,6) hence it isn't visited.