Don't call me son, I'm probably older than you. Haven't spoken to Mom much in the last 20 years or so, so I wouldn't know that either.
Anyone buying a case doesn't do it blind, they'll look at it first, read the info online, read the Amazon junk etc so no, not the install directions as you assume, until they do buy the case and it tells them that because they bought a case with a side dust filter (which 98% of cases don't include) that it should be used as intake. It's no different than some cases use red leds as intake fans, you'll see it in the pictures, you'll see it printed 'comes with led fans!', like that really makes a difference, it's just something to distinguish the case from others, a selling point.
And yes, I actually did dig up the manual on my old CoolerMaster 690 II Advanced and it says quite clearly that because the 2x fan slots on the case side are unfiltered they should be used as exhaust.
Nzxt H440, has 3x 120mm intakes in the front, written in every advertisement you see that because of its 3 fans it has excellent airflow and cooling properties. That's the manufacturer talking. Reality is the H440 has pretty mediocre airflow and cooling properties. That's the expert reviews and pretty much everyone other than the manufacturer. Just because a manufacturer makes claims, doesn't mean they are gospel. And shouldn't be taken as the full truth. Side fan vents should be used as exhaust in most pc's, unless they are filtered for intake or the gpus temps are far out of control otherwise.
My grandfather was a 'prop man' in WWII, my father is a flight mechanics engineer, and I'm a retired fire-fighter/arson investigator, so I've been around airflow and thermal dynamics, it's patterns and properties my whole life. I'm not an expert because I'm some Joe-Blow-on-a-forum who read it in a post, I'm an expert because I am.