What's with the missing boss fight in the Matlan Waterways?

Towards the end of the Matlan Waterways, there's an area that appears to be an unused boss arena. Most notably, while standing inside it, your town portal button is disabled, with the popup text "Portals are disabled in boss fights". There are two groups of hounds chained to the walls of this area with no human NPC holding them.

Just wondering if there was a boss fight here in prior versions that has since been removed, or if this was content that was cut somewhere along the development process.