Yeah it seems like a remaster. Or more specifically via a re-implementation as a sort-of official mod for Age of Empires 3 (thanks for the correction) I imagine, and judging from the graphics.
The Extended Edition was like the HD Edition of Age of Empires 2 (now called "Age of Empires II (2013)" on Steam). This is more like the Definitive Edition. Significant graphics improvements (as opposed to just taking the existing graphics and upscaling them), as well as new content and probably QoL improvements.