The idea is not that those who haven't gone to university don't know better, but that going through university (which is assumed to have and take seriously an academic integrity policy) would teach them (even though many would already know better). To say that something is typically true of members of a group does not mean that it is typically not true of non-members.
Yes, this. There isn't really a single avenue of study at University you can choose where you shouldn't encounter this. Unless you can make it through a degree without writing a single paper. The idea that you can plagiarize anything in any context at all is basically anathema in almost all academic circles. Not that it doesn't happen, but most people that even attempt it are smart enough to do more than change the font size to hide it.
I did a BSC in Computer Science at University. About half my class failed our first ever programming assignment because of plagiarism. Loads of people had just shared the code between them, character for character. There were a few cases where they even left the original authors name in the comments at the top of the code.
Instances of plagiarism dropped after that. At least they learned how to change variables, function names, comments and whitespace enough to get around the automated plagiarism detection tool.
