I tried as suggested by Abdul Khan above but
DataSource ds = DataPoint.getOriginalDataSource();
String streamData = ds.getStreamIdentifier();
/*I also tried but could not achieve what I wanted*/
String packageName = ds.getAppPackageName();
String streamIdentifier = ds.getStreamIdentifier();
did not work at least for me while retrieving data. I ended up using readDailyTotalFromLocalDevice() as shown below in order to capture steps captured by device only.
Fitness.HistoryApi.readDailyTotalFromLocalDevice(mApiClient, DataType.TYPE_STEP_COUNT_DELTA).await(1, TimeUnit.MINUTES)
I cross checked the same with some of the apps that avoids manual entries in their app and the count provided by the function above is exactly the same.
Note: If a user is having multiple devices and is using the app on all of them, readDailyTotalFromLocalDevice() will have different value for each and every device since the function is responsible for returning device specific data only.