We like to deploy a template project as soon as the jam starts just to check it's all in working order (TheChief intentionally always tries to be the very first person to have a submission up). Sufficed to say everything was actually built specifically for the jam and we have receipts - new builds going up throughout the jam and plenty of discord messages with WIP mockups/recordings. :)
I agree that it looks suss though - I don't know why itch highlights the date of the initial submission rather than the most recent one. As for the page existing before the jam was up, there's nothing to stop anyone from making a holding page for their game before a jam starts, as far as I know.
(image from TheChief from several days ago, hence why 'yesterday' is 2nd August)
