Are you referring to the forum timestamp that pops up when you click the time indicator at the top right of your post? I am not seeing July 16 on your post; I’m seeing July 19:
Oh, you are referring to the topic post count slider over to the right side? The date of the topmost post any part of which is visible on the screen. In this case, you have a little bit of the post above Wendell’s showing and that post is dated July 15.
By the way, there is sometimes a mismatch between the post #s on the slider and the post. This is due to hidden/deleted posts that you can’t see. I’ve brought this up with Discourse to consider fixing.