It’s unfortunately become a catch-all phrase meaning “this is hard and you’ll die a lot, git gud lol.” In this case though, there’s a lot of parallels between Dark Souls and Hollow Knight on multiple levels: Themes, gameplay and design philosophies, how lore is dispersed… I can’t really elaborate without going into a ton of detail and spoiling things, but needless to say, there’s an actual reason for that tag here. I would also say that, while there isn’t a specific “easy mode” to switch to, there are different ways to tweak the difficulty while you play. Charm loadouts, putting extra time and effort into finding hidden power-ups (health expansions, for example), and the fact that some of the most challenging portions of the game are basically optional unless you’re looking to experience every piece of the lore personally.

I personally don’t see any problem with just looking stuff up after playing the game if you’re satisfied with the experience you had, but your mileage may vary there - I don’t have as much time to spend on gaming, so my tolerance for grinding or bashing my head against a challenge repeatedly is directly tied to how fun the actual gameplay is for me. I was much more tolerant of the difficulty in Hollow Knight because the controls are so tight and responsive that it’s just fun for me to play and improve in.