The argument confuses sufficient and necessary conditions. Only M cures athlete’s foot, making it necessary for curing athlete’s foot in the study. However, that doesn’t mean it’s sufficient to always cure athlete’s foot.

The reporter only draws a conclusion about the study, not the population as a whole.

The reporter doesn’t make any claims about the availability of the medications, only their effects on athlete’s foot in the study.

The reporter is only drawing a conclusion about the efficacy of medication M based on the study, and doesn’t need to account for the possibility that athlete’s foot could be cured in other ways.

The reporter is only discussing the study, where every participant whose athlete’s foot was cured had received M. The possibility of this kind of subgroup is irrelevant to M being necessary to cure athlete’s foot in the study.