You are waaaaaay under estimating that figure.
Basically every Louisiana citizen born before 1967 claims to have been there -- not only that, they all claim to have been sitting in the end zone that Gilliam ran towards.
There's a similar attendance legend with the LSU Billy Cannon Halloween Punt Return. If you were born before the 1950s in Louisiana, you were in Tiger Stadium that night. If you were a boy between the age of 7-14 in 1959, you were a Cub Scout/Boy Scout working as an usher at that game and/or working at a concession stand.