19COBRA93
Ford Racing
I used to think like you do. I installed Scott Drake hood pins for looks but having left the pins out because I didn't want them stolen (the retaining cables rusted) had my hood pop during a "high speed" highway run. Fortunately the safety catch worked but the pucker factor nearly tore the leather from my seat.
Everything checked out with the latch and the stops are properly adjusted, but it still popped. The car only had 19k miles on it.
Now the pins stay in...
I'll bet your hood just wasn't latched all the way. If the OEM hood is latched properly, you can tug, pull, pound, and struggle with all your might, and you'll destroy the hood before you'll get it to open on its own.
I've shut my hood before without it being latched. It looks closed, but it's not latched entirely. That's the only explanation for your incident. The hood latch works exactly like a door latch. Ever had your door pop open? Me either.