A redshirt can be a non-scholarship athlete. A redshirt can also be a true non-recruited walk-on. The term "redshirt" simply means that a student-athlete did not use one of their four seasons of competitive eligibility during that season.
Yes, it can be semantics. Sometimes it's just "coach-speak." Just like how the term "preferred walk-on" only means whatever that coaching staff intends it to mean in their mind.