It's important for HR to respect the personal privacy of ALL parties in an investigation and maintain confidentiality regarding disciplinary matters or personnel actions to the extent that it is practical and appropriate. Thus, you may never know the outcome of an investigation beyond that "the matter was appropriately handled."
Some personnel actions may be obvious to you. For example, the person complained about (PCA) is discharged from their job, demoted, or transferred to a different department. Other serious personnel actions may not be obvious to you. You'd have no idea they took place. These might include a cut in pay, loss of a bonus or other form of compensation, formal write up to the PCA's personnel file, a coaching or counseling session with upper management or HR, or remedial training.
This doesn't mean you shouldn't be alert or concerned. If the offending behavior repeats itself, certainly report it again because the action wasn't sufficient.