When I see this, I always start to think about my grandfather, who was a sailor in the Navy, and never went to university. He was, however, an educated man. Not in the university mode, but a type of person that I haven't encountered for some time but which seems to have been common. He had practical skills, but he knew his history and political theory cold, he was well read (Kipling was his favourite author, and Burns, but he read everything,) he was a beautiful writer and a stickler fr grammar, and he wooed his wife by writing her not bad poetry. And he wouldn't let anyone get away with less than a watertight argument which made him annoying.
This used to be very common within working-class communities, where education was seen as a form of intellectual development which you acquired, rather than an externalised process which was imposed upon you. This massively shaped both working-class communities, and society in general, throughout the nineteenth and twentieth centuries.
Mechanistically, this is a very open-ended approach to education, which has a significant effect on what you do learn. If, for instance, you study within a formal educational setting, such as a school or university, the direction and scope of your learning is shaped by formal curricula or course requirements. You learn what you need to, and generally no more, and once you have finished a course, you have no need to return to it. For those not familiar with theory in this area, this is generally called the inoculation theory of education.
If you are, instead, going down the autodidactic route, there are no sharp definitions to what you are looking at, and no inherent end point. People who take this approach will invariably learn more and, perhaps more importantly, make connections between different types of information that will not occur within formal educational settings, where knowledge is sharply delineated by subject.
There's a really good book about the history of working-class autodidacticism; "The Intellectual Life of the British Working Classes", by Jonathan Rose. Reading the book makes it clear how heavily the notion of ownership of learning and information has shifted in the last century, and suggests (in my mind at least) one of the reasons for some of the problems in institutions we face at present.