فَإِنْ صَلَّى النَّاسُ وُحْدَانًا جَازَ، وَإِنَّمَا الِاسْتِسْقَاءُ: الدُّعَاءُ وَالِاسْتِغْفَارُ.
Translation: If people pray individually, it is permissible; istisqa itself consists of supplication and seeking forgiveness.
Wuhdan means praying individually. The term jaza establishes permissibility of individual voluntary prayer. The point denied is a fixed congregational sunnah form.
Permitting an act individually and recognizing it as a prescribed congregational sunnah are separate legal questions.