Is this a mammillaria bullardiana?

Hi Sonje,
I think that this is what is now known as bullardiana, so I think yes!

There does seem to be some confusion about this plant vs the original description by Gates. The original description of M. bullardiana calls for 1 central spine (OK here) but 20-30 radial spines. I can't see clearly enough the numbe ron your plant but I'd say a bit lowerin number than this. But it does have the pale pink flowers as described, and that your plant is showing so well.
When Reppenhagen described it as a subspecies of hutchisoniana he commented about the discrepancy of the radial spine count, as his description has only 15-17, and he says that this is the right subspecies because of its geographic location (La Paz) and the nature of the soil it grows in.
Hunt simply lumps it in as a form of hutchisoniana, and comments regarding hutchisoniana that even with this species there is a discrepancy in spination, both central and radial, between many of the plants found and Gates' original description, concluding that it is a highly variable species and so doesn't accept the subdivision.
What is true for me is that it is distinctive, especially when in flower and its pale pink flowers certainly show a contrast to the creamy colour of hutchisoniana.

Thanks, Chris for the information.