HI
interpersonal skills are linked to your behavioral perspective.
An engineer is better equipped to analyse any situation using his analytical and logical acumen. When a person is moved to next level of hierarchy, they are made to go through a managerial training session where they learn the managerial tools in which the major stress is on their interpersonal skills as the main job of manager is to get work done by people, for the people keeping the interests of organisation ( which again constitute of people).
Hence, from my perspective its the attitude of person you deal with not engineering skills or management skills.