the coding is undoubtedly taking the last change date and user from the SY structure:
IF NEUFLAG NE SPACE.
MARA-ERSDA = SY-DATUM.
MARA-ERNAM = SY-UNAME.
ENDIF.
ENDIF.
And this sounds logical to me, as if this would not be the case, then you could change data with an IDOC and let it look as if this change was done by someone else.