SSIS is a client service / tools, so it will work where the package is physically located.
In your case, the SQL Agent Job on ServerA runs only the package, the package located on ServerB . All data processing and data flow occurs on ServerB .
A package itself can have many connections to flat files or databases, but all data from these flat files and databases will flow to ServerB , not ServerA .
I hope this answers your question and eliminates any confusion.
M.Ali source share