وَإِنْ قَدَرَ عَلَى إِدْرَاكِ أَحَدِهِمَا: فَلَيْسَ بِمُحْصَرٍ.
Translation: If the pilgrim can attain either of the two rites, that person is not classified as muhsar under this rule.
The dual pronoun ahadihima refers to the standing and the tawaf.
Being unable to reach both is different from being able to reach at least one. The text here resolves the classification as muhsar; it does not say that access to one rite automatically completes Hajj.