I am also only humble SLF (but who will fly over 100 sectors this year, long and short haul) but take a keen interest in aviation. Hence being registered on here.
As someone else has eloquently pointed out, when crew make mistakes we are all asked to think about "human factors" and how "all the holes in the swiss cheese line up". Clearly the same should apply here.
Most people, if you ask them to think about an emergency evacuation, will think about going down slides. That's what you see (and focus on) in the safety briefing, and that's the image you get when TV pictures show an evacuation. It is what your mind "expects" to see when you need to evacuate.
The safety cards are often not explicit in stating that there is no slide from the overwing exits (for those types where there isn't one). As far as I can recall, I have never seen an explicit reference to sliding down the trailing edge in a video, demonstration or on a safety card (and I have flown many types of metal, with many different airlines). I can only recall it being specifically mentioned once in a personal briefing when I was in the emergency exit row.
Are you seriously expecting an infrequent passenger to look at a picture on a safety card, notice that a slide *isn't* there, and then realise that they are meant to slide down the flaps instead?
Comments about being moronic or stupid don't help when the information provided is clearly not sufficient.