Integration Services :: Merge Inner Join Gives Different Output Based On Sort Key?

In the first image as can be seens i have 2 different data sources and then they are being joined using "Merge Inner Join". The "sort" is on BusinessEntityID column of Person table and "Sort1" is on "PersonID" of Customer table. The merge join of these 2 result in 19,119 rows.

On the other hand, if i use single data source and use a query with inner join on  tables  used in the first image (ie. 2 tables being used in 2 different data sources) as depicted in second image. Also,  since merge cannot operate without SortKey i have defined TerritoryID as sort key in the advanced editor. The number of rows i get after this is "10,274". My select query was :

SELECT
P.BusinessEntityID,
P.PersonType,
P.Title,
P.FirstName,
P.MiddleName,
P.LastName,
P.Suffix,
C.TerritoryID
FROM stg.Person AS P
INNER JOIN stg.Customer AS C ON C.CustomerID = P.BusinessEntityID
ORDER BY C.TerritoryID;

According to me, it should have been the same as in first case i am using merge inner join and in second case i am using SELECT query with inner join. Upon drilling down i found that in the first case , my sort keys are BusinessEntityID  and PersonID, if i modify this to CustomerID  and BusinessEntityID as this is my join condition (in ithe inner join query shown above), i get the desired output. What i was wondering was, how  the sort order change the Join Condition?