It does imply lack of access to formal resources, though. Learning from a textbook or an educationally-minded Youtube channel is no more self-taught than sitting through a lecture in college.
It is ultimately a distinction without a difference. Historically, when information was siloed, there was a difference. Self-taught meant something when you couldn't look something up on a whim. But those days are long behind us.
Going to the library or buying and reading books is not formal instruction, and neither is watching Videos. There is no one to guide, help, or check on progress.
I could watch the entire MIT Intro to Algorithms Course on YouTube and still be self-taught, because watching that does not make me an MIT Student and it does not make Dr. Jason Ku my instructor.
Most people probably do this. These types of discussions (probably) come up when someone else made the choice and other people also need to adhere to this choice. This is important for teams, but sometimes big egos don't want these choices made for them.