Scholarly disagreement:

The jurists differed over whether dry ablution (tayammum) is required for the limb covered by a jabīrah.

The three Imams—Abu Hanifah, Malik, and Ahmad—held that wiping over the splint alone is sufficient; no tayammum is obligatory alongside it.

Imam al-Shafiʿi, however, maintained that one must perform tayammum for the area beneath the jabīrah in addition to wiping over it.

The first opinion is the sounder one, for a substitute act should not be combined with the act it replaces.

It is most likely this Shafiʿi position that led the author to cite the present hadith here.