Li’l Abner wasn’t just any old comic strip; it was one of the most influential American comic strips of the mid-20th century. It had multiple imitators, movie and musical versions, and even a theme park (one that I remember some of my friends visiting in the 80s). It launched Sadie Hawkins Day, and it took on political and social commentary more than any other comic strip before it had. When the two main characters in the strip got married the event made the cover of Life magazine. I think Li’l Abner was even largely responsible for the “backwoods country folks” genre of American entertainment that was popular for a few decades (think The Beverly Hillbillies and Hee Haw). It was kind of like the Calvin and Hobbes of its day - except that, since Al Capp was much more of a self-promoter than Bill Watterson, it manifested itself in many more parts of American culture.
So even if you hadn’t heard of it specifically, it doesn’t surprise me that some of its characters and themes found their way into your head from other avenues. 