Note that Tom Scott’s video is about the Uffington White Horse and the horse in OP’s post is the Cherhill White Horse.

https://en.wikipedia.org/wiki/Uffington_White_Horse

The Uffington White Horse was created some time between 1380 and 550 BC, during the late Bronze Age or early Iron Age.

https://en.wikipedia.org/wiki/Cherhill_White_Horse

The figure was first cut in 1780 by Dr Christopher Alsop of Calne, who created it by removing turf to expose the underlying chalk.