Until the day when BCA mandates that BIM managers should possess a Specialist Diploma certificate, the qualifications of BIM managers are still vague. Anyone can "grow" into a BIM manager with some form of self-study and effort to do their own skills-upgrading.
While googling, I found an interesting discussion on LinkedIn with professionals in the field offering some insights to what a BIM manager do: https://www.linkedin.com/grp/post/68075-112896065
In short, it is not about the software. It is about the management of the workflow, processes, and people working with the software. Because every company uses different software, technology, systems, the BIM manager is responsible for such collaboration, project teamwork with different disciplines/companies to work. BIM management goes more into project management and requires both architectural and technical expertise. Being a BIM manager is not easy, as once you list out the responsibilities, you will see why. Poster #2 puts it succinctly:
They need the skill of understanding the company they work for; a realization of the goals that need to be achieved; the ability to manage individuals (even if they are not direct reports); the "skill" of discovering better / creative ways to achieve goals; the intelligence and communication skills to quantify and communicate the value of these achievements within the organization.
Is the time spent going through the Specialist Diploma worth it? I should be able to tell in 6 months time.