[CentOS] Mysterious versioning reported by file command

I just noticed this, which doesn't actually seem to affect anything but does
create a mystery:

[frankcox at mutt temp]$ cat test.c
#include <stdio.h>
int main(void)
	{
	printf("Hello world\n");
	return 0;
	}
[frankcox at mutt temp]$ gcc -o test test.c
[frankcox at mutt temp]$ file test
test: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked
(uses shared libs), for GNU/Linux 2.6.18, not stripped
[frankcox at mutt temp]$ uname -a
Linux mutt.melvilletheatre.net 2.6.32-220.17.1.el6.x86_64 #1 SMP Wed May 16
00:01:37 BST 2012 x86_64 x86_64 x86_64 GNU/Linux

Why does the output from file say "Linux 2.6.18" when the actual kernel in use
is 2.6.32?

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