Not that strange. There are several orienteers who are noted for swearing to themselves the whole way around the course.
Well, I don't recall swearing that much, but that is good to know. I hadn't noticed these orienteers yet.
Talking aloud can help focus. Some people might be less likely to wander from the task at hand. In orienteering races, I've found myself more distracted at times than I'd like. This tactic has helped considerably.
Many years ago, I recall a then prominent orienteer finishing up a West Point meet. There was some kind of "sleight of hand" in control description or numbering. I heard a blue streak. Volatility varies among orienteers too :-).