Now that would be reasonable if there were actually tweets that had been tweeted since I visited the page. Except the newest tweet on the page before clicking that was 18 hours old, and the newest tweet after clicking that is 7 hours old. And no, I did not wait 18 hours - the link appeared under a minute after loading the page.
So there weren't any new tweets. But what there was is the tweets that Twitter for some crazy reason of its own decided not to show when I visited the page.
It's not client-side caching as I've not visited that account for days if not weeks. It's not server-side caching (or if it is it's very broken) as I seriously doubt that no-one's looked at the LulzSec account for 18 hours. There is no usability reason for doing this. I can't think of any reason why one would want to make the backend behave like this.
Presumably this bit of unusability came from the same place that the idea of using the hashbang in URLs (which means that you don't see individual Twitter accounts in your browser history) came from.