Granted my view on it is entirely subjective, but how else would you define the horror genre? What exactly would be the genre defining tropes? Monsters? Plenty of games have monsters of various scary or terrifying persuasions. The way you control your character? That's a sliding scale if anything and has changed troughout the years. The only constant element of the genre is the need to be scary, if it isn't scary it's an attempt at a horror at best.
As far as CSGO goes, it's why I said contextual, because stratey in the context of videogames has, as far as I can remember videogames been always associated with the RTS/TBS/GS genres and their permutations. The same goes for horror games, while the exact device has shifted over the years from stuff like Silent Hill to the FNAF craze of recent years the one constant has be the scary bits.
I do realise that this may seem contradictory to some extent but I honestly think that different genres deserve different views on what qualifies a game for such a genre. While horror is entirely subjective, something like RTS isn't and I think it's mostly down to the fact that horror isn't so much a genre unto itself as it is a theme for any give genre. Same as comedy, romance and what have you. You don't have it standing on it's own two feet because it has none, instead it piggybacks on other core genres to enhance them to one degree or another. It's why RE4 is a
survival-horror where the focus isn't on shitting your pants because scary monsters, it's shitting your pants because you're trying to stay alive troughout it all and the monsters themselves could be anything, but the core game would still be a survival TPS.
(unrelated, but writing this has actually made me properly coalesce my thoughts on the matter for the first time ever as it was always a sort of stance but since it never got properly challenged I never had the chance to hammer it out into something concrete, thanks Neo
)