It's not. The photos with the horizon visible are photos taken during the descent, whereas the photos with only ground visible were taken as landing was imminent (or after landing).
There is a photo on the page that shows the horizon from a landed position, that's the one he's referring to.
It links to, and is displayed, here; with no indication that it's an artist's take on what it would look like. It seems to be D. Mitchell's stitching work from this Venera-13 clear-filter panoramic transmission with added perspective from the color-filter panoramic transmissions.