Multi part identifier in Microsoft SQL Server
As you say the query doesn't make any sense.

Probably just a parser bug in 6.5. There have been a few similar other issues ORDER BY nonsensealias.somecolumn worked until 2005 with the SQL Server 2000 behavior being


  Column names in the ORDER BY clause are resolved to columns listed in
  the select list, regardless if they are qualified. For example, the
  following query executes without error:


USE pubs
SELECT au_fname AS 'FName',
  au_lname AS 'LName'
FROM authors a
ORDER BY a.LName



  SQL Server ignores the qualifier a in the ORDER BY clause and resolves
  the column name LName to the select list.


and there is still a similar issue for INSERT statements where the following syntax is accepted.

CREATE TABLE nisse(hult int NOT NULL)
go
INSERT nisse(ab.xx.hult)
VALUES(12)
go
DROP TABLE nisse