Habitable real estate explains the planet's value to the ECA, but not why the company would co-finance it for minerals that could be more easily obtained elsewhere.
Of course, it's possible that the company had the same question that I do: what exotic substance could such a tiny planet contain that would give it such a strong gravitational pull? Maybe they don't know any better than you or I do and that's why they wanted to secure the mineral rights.
That's the most non-committal explanation I can think of that both addresses the point and evades a definitive answer.
