as someone who's joined a couple jams before I don't think your missing anything I think the guy just forgot to update the theme. If there's a discord for the jam (which usually is the case and is linked on the jam page) you can ask or maybe it's only been updated for the discord server. But idk so I'll take like 3 second to check and edit my reply
Update: no server. I'm not sure about the jam-holders timezone so maybe they're just asleep and will probably wake up soon
