Was his rep red when he gave it, or was his postcount under whatever the default number to pass is? Often those who play by the "don't open your mouth unless you have something to say" rule have very few posts, thus often take months or years to exceed the post limit.
The final thing was he might have posted rep, but something happened to the post (deletion, locked thread, moved to a mod's only club, etc) that would grey it out.
I have no clue what default is for Vbull, since I never started a forum up before....so the magic post number for rep to count can be 10, 100, 1000, 666, whatever the default is or what the mods set it to really.
These systems are far from perfect....it will all make sense as time goes by.
EDIT: Sheep, what color was the rep I gave you? It's supposed to be green. I was being a moron and gave it under a name I use on another forum --catatonic