Doesn't surprise me, about not knowing there were aiming systems. Most players don't know. Unless you're an online guru searching Google for "pool aiming system", or active in online billiards forums, you'd have no clue about anything other than what you can gather from local players or local bookstores.
The internet has only been around since the 1990's, and it wasn't too widespread on availability then, so about any pool player that had a decent game prior to that wasn't necessarily shopping online for learning or improvement methods, and most of the millions of pool players around the world had never heard of Hal Houle or any other aiming guru.
Even today, if you go into any pool room and randomly ask if anyone has heard of Hal Houle, you'll more than likely get, "who's he?", unless you just happen to find one of the few thousand or so online forum members that follow such things. I mean, I think AZ has about 160,000 members, which is a thin slice of the total amount of pool players in the world, and of this 160k membership many are not following aiming or instruction forums. So it's no surprise that the average player is more or less self-taught with whatever resources can be found locally.
I’d heard of Houle several years ago on the Billiard Digest site but his technique was never really explained in the detail you see today via diagrams and videos.