The thought was that the higher your intelligence, the higher the chance you know what you’re seeing. So if you have a high intelligence of say 19, then you need to design the check such that it’s very likely you’ll “succeed” in recognizing it, so with a D20 that means rolling under 19 (a 90% chance). A lower intelligence would actually be a good thing in this case, someone with an intelligence of 2 only has a 5% chance of “succeeding” and rolling under a 2.

It could be, I only ever played the system once and I’m not really familiar with the rules. At a glance, it looks like the intelligence roll usually happens after losing a certain amount of sanity?

I played a one-shot of Call of Cthulhu where the DM had you roll an intelligence check if you saw a horror. If you rolled over your intelligence, you had no idea what you were looking at and were unaffected. If you rolled under your intelligence, you knew exactly what you were looking at and had to roll against your sanity to see if it drove you insane.

In other words, you could have no idea what you’re looking at, know what you’re looking at but handle it, or know what you’re looking at and not like it!