[CentOS] Strange Kernel for Centos 5.5

Thu Feb 10 21:25:24 UTC 2011
Always Learning <centos at g7.u22.net>

One of my VPS stopped working. After the data centre replaced a disk
normal service resumed, then I notices this:

CentOS release 5.5 (Final)                                                      
Kernel 2.6.35.4 on an x86_64

I always thought Centos 5.x would always be on 2.6.18. Any thoughts?