That is correct. 16 has never beaten a 1, but a 15 has beaten a 2 at least a couple times. Last one I remember was Hampton beating Iowa State (Marcus Fizer / Jamal Tinsley) Tinsley tried to go Tyus Edny at the end of the game but the layup rolled off the rim.
the closest a 16 beating a 1 seed was I think albany given Uconn a run for its money a few years back. I think uconn had to win that game on the final poessesion