Shenmue 2's Hong Kong isn't the biggest of open worlds, and unlike the Yokosuka suburb that preceded it, it can hardly claim to be the densest.
Considering these were pretty much the first open world games, that comment is a bit unfair. Of course they are no longer the biggest, but at the time they were.
The author isn't talking about Shenmue as a game from a past point of view but as a modern game, and that's why this article is way more interesting than any other articles explaining why Shenmue was so revolutionary at its time (that no one cares).