There's also a "curator effect" that some teachers take to heart, if you can call it that, in the sense that if it wasn't taught by them, you shouldn't know about it, or that knowledge is suspect in some way.
Going back to ancient times, my class on Applied Programming used Lotus 1-2-3 macros to develop an automated spreadsheet. Our professor insisted that we use /X commands, which were cryptic and made debugging difficult. My cousin loaned me a book which explained that the /X commands could be replaced with commands in braces, so /XBG would appear as {GOTO}, for example. My code became much more legible and easier for anyone who came afterwards to follow.
The professor, however, refused to accept any assignments that used the brace variant of these commands, even though they were legitimate and functionally identical, simply because he hadn't taught them. After all, I could have "cheated" by obtaining knowledge that wasn't available to others in the class. That was one professor that lost a lot of respect in my eyes. As someone who's been on both sides of the teaching relationship, I would regularly take pride in those that exceeded the scope of my classes, and that went above and beyond what we could cover in the classroom.