I dette tilfælde er den afledte tabel, der kræver et alias, den, du vælger * fra.
Indrykning hjælper med at gøre det tydeligere.
SELECT * FROM
(
(SELECT '1' AS `table`, `vid_req_timestamp` AS `timestamp`, `title` FROM `movies` WHERE `vid_req` = '1')
UNION
(SELECT '2' AS `table`, `ost_req_timestamp` AS `timestamp`, `title` FROM `movies` WHERE `ost_req` = '1')
) AS `some_table_name_lol_this_is_an_alias`
ORDER BY `timestamp` DESC