No, no, no! The OP is talking about the block on the home page which shows who's on, and it's been screwed up for a couple of vBulletin releases now. DavidB said it was a problem with the software that he couldn't fix. It's backwards, that's 85 guests and 500 members, to use the OP's example.
EDIT: Which is wrong, too--right now the home page says 115 members and 473 guests, but if you click on the "online users" link, it shows 115 members and zero guests. I must have been thinking about something before the last upgrade was backwards about the online status, this looks like it's showing all the guests that have been here in the last reporting period, whatever that is (day, week, etc.).