"Tracking" generally refers to third parties identifying you across websites.
Pointing out that Reddit "tracks" you with its authentication system as you browse Reddit just dilutes the term and the gravity of concern when organizations are able to connect your browsing history to you.
Put another way, a "has_gold" boolean field in the users table doesn't seem to be the issue that the EFF is attempting to address here.
That's sort of the point, though. Is there anything in the "do not track" policies that prevents the data owner (Reddit in this scenario) from just selling its own scraped data on the end-user to an ad network? Ad tracking is functionally equivalent; the tracking scripts just automate and simplify the process.
"Do not track" is a bit of a toothless concept when the very nature of the medium is to make auditable connections to remote servers.
I don't know whether they do it, but they could set a http-only cookie "gold=true" when you purchase a gold account. You could then logout and they would not habe to track you personally to check your gold status.
