I just checked again to be absolutely sure (I think I have done this previously as well), and it's 100% for sure Hdeg 4:3, not vertical.
I know it even says "vertical" in the info section when you set the FOV in-game, but it is wrong.
My best theory is that to not "confuse" players with unknown jargon, they just say the FOV is vertical (since the vertical FOV stays the same regardless of aspect ratio) and hope no one notices/cares.