The Wing Tsun wooden dummy is thought to have originated in the Shaolin 108 Wooden Man Hall where a trainee of the Monastery would have to navigate down the hall as his or her final test. By the way, women were not ordinarily permitted. The story of the female elder has that going against it as far as credibility but that is another topic.
The trainee would have to “fight off” a dummy when it came out of the wall. He would accidentally trigger them by stepping on certain planks in the floor.
Wooden dummies were, like chi sau, probably not invented but rather developed through history. Several martial arts have their own versions of wooden dummies as part of their ancient history. It seems likely that a wooden dummy as a training device could have originated in the same place. The other possibility is that one martial art took the idea from an instructor of another martial art and adapted it for his own use and teachings.
As a reinforcement of the authentic historical origins of wooden dummies, several other Chinese martial arts also use wooden dummies of different designs.