vBulletin converts tabs to spaces. Even if he had used tabs, the post would still display spaces.

Incorrect. Behold!

I concede, however, that it may be possible your web browser is converting tabs to spaces. Mine does not.

Never has for me, whether using Chrome or Firefox.

I was more directing that toward the [highlight="Lua"][/highlight] tags that everyone is demanding code be used in. Every one of them I've used converted to spaces and I always use tabs. It may not be all of vBulletin as I had thought, but it's certainly doing it somewhere in the system.