Also, it sounds like you're worried about conflict of interest since this person doesn't report to you. Would it make sense to approach their manager with something like: "I've noticed EmployeeX doing X at work. Have you noticed that too?" That helps see if you're in alignment with the employee's manager. Maybe the other manager has reasons for encouraging or tolerating that behavior. That's important for you to know before you offer to change it.
If you are in alignment then something like "It reminds me of a situation I was in earlier in my career. Do you mind if I ask EmployeeX if they'd be open to some coaching around the issue?" That way you get everyone on board.
Transparency and honesty will usually help diminish people's fear of "interference". And if the manager or employee aren't willing to accept your help or see things as you do, then it's better to accept that and focus on your role and responsibilities.