Last week a video was posted on youtube showcasing a graphics comparison between Horizon Zero Dawn at the Tapei Game Show 2017 and E3 2016.

Although the video quality differed, there were still a few visible changes compared to E3 2016 such as changes in lighting and missing foliage, leading people to speculate a downgrade.

Guerilla Games put that to rest in a tweet stating that the gameplay from both the videos are from the same build and that there has been no downgrade.

Actually both videos are captured from the same build; one running in English and the other in Chinese. — Guerrilla (@Guerrilla) January 25, 2017

We've seen the comparison video you refer to, but we can assure you both captures were taken from the same build. — Guerrilla (@Guerrilla) January 25, 2017

That being said, in the gaming industry many developers do lie and manage to get away with it with little to no slack – the proof will be in the final product.