An earlier ticket (SERVER-112725) checked for non-existent collections in executor.cpp and the same check also inadvertently passed for sharded collections. As a result, the tests in lookup_sharded_no_join_opt.js passed for sharded collections even without my new code because this check is triggered in executor.cpp
if (mca.isAnySecondaryNamespaceAViewOrNotFullyLocal())

{ // TODO SERVER-112239: Enable support for views, as the above check will prevent views from // being used for join ordering. return false; }

The correct check is to check if sharding is enabled on any of the foreign collections. The test now passes with my code as my new check is correctly triggered.