I'm not talking about someone posting in the thread. Anyone who comes to post in the thread of a TV show they aren't current on is asking for trouble. But the thread title is visible to everyone and during the shows run it pops up on the first page of the OT section quite often. So someone actively avoiding the thread until they are caught up can still be spoiled by a title. If a person is avoiding the thread because they aren't caught up (ie me), they aren't going to know about memes and typical posts in the thread.
You aren't strengthening your argument by introducing a hypothetical person who knows
even less. A person who has no point of reference for the season also wouldn't be spoiled by the thread title.
At this point you're suggesting a person exists that:
1) Wasn't currently watching the season, but saving for a later time.
2) Yet knows enough about the new season that Savitar is the main bad guy.
3) Doesn't know enough about the Flash to know that "It was me, Barry" is about the Reverse Flash.
4) Yet assumes that a line of dialogue in quotes is actually not a line of dialogue and is some Lionel Hutz style "No, money down!" type typographical spoiler.
Why would this person assume the title is not just something Savitar said? A revived Eddie could have said this line. HR could have said it. Without context, without already assuming Barry is Savitar, it is just meaningless.