Webflow’s default date fields don’t mean which you think they should.
Notes on that here.
The reason your date field isn’t matching the Original Date of the page you’re on is that you’ve placed it inside of a collection list, which is also bound to Blog Posts, but is filtered. You’re getting different data inside that collection list than you are on the page overall.
Pull that date field out of the collection list to the main page level, and it will work fine.