I would speculate that this is a large mercury-like planet with no atmosphere. We still don't have enough precision in our measurements to account for earth-mass planets. There could be other planets in this system that could be in a habitable zone. It will be interesting to see what we find when we attain enough precision to find smaller planets around stars, I still think our stellar neighbors Alpha Centauri A&B will have some surprises.
Alpha Cen A is slightly larger and brighter than the sun, and Alpha Cen B somewhat dimmer but both are well within the range that most astronomers think would easily support Earth-like planets at the right distance.