The English translation of the verse is misleading. A more precise translation would say "those (ideas) that are against the Sūtrakāra are rejected". The short commentary below the verse in Sanskrit clarifies, 'sūtrakāramataviruddham' - "they are against what the Sūtrakāra intends."
- As we shall see, this is not literally rejected by the Sūtrakāra
but rather by the Śrībhāṣyakāra Rāmānuja.
- It would also be more appropriate to translate Saṅkhyā as 'Count'
rather than 'number' since it really means cardinality of a finite
set in this context.
- The short commentary for the verse also says that the limits of
reasonable consideration of these qualities (Saṅkhyā, etc.) are
described in Chapter 10.
The relevant sūtra is Vedanta Sūtra 2.1 A(6) S(15) in the Ārambhaṇādhikaraṇam
तद् अनन्यत्वम् आरम्भण शब्दादिभ्यः
tad ananyatvam ārambhaṇa śabdādibhyaḥ
From the passages beginning with "ārambhaṇa", it follows that the
Universe is not different from Brahman
In the Śrībhāṣya, Rāmānuja devotes significant space to discussing this sutra. Only a tiny fragment of it is relevant to your question, so I am only quoting the relevant passages and explaining them here:
One of the opponent's arguments is that since souls are distinct from each other, the number of souls has to be finite. The analogy given to support this is: Objects like grains, seeds, pots, clothes that are distinct from each other are also seen to be countable. Thus, the opponent argues that Count is an essential property of entities that are mutually distinct.
घटादीनामप्यनन्तत्वात् दृष्टान्त साध्यविकलस्स्यात्, ...
ghaṭādīnāmapyanantatvāt dṛṣṭānta sādhyavikalassyāt, ...
Rāmānuja's counter argument is that while the property of Count makes sense for ordinary objects like seeds, it is only an emergent property that arises due to the limits of space and time imposed on ordinary objects. If there are no such limits, then no such emergent property can arise. Therefore Count itself is not a quality inherent in the object.
... दशघटा सहस्रं माषा इति सङ्खयावत्त्वं दृश्यत इति चेत्-सत्यम्, तत्तु न घटादिस्वरूपगतम्, अपि तु देशकालाद्युपाधिमद्घटा-दिगतम्,...
... daśaghaṭā sahasraṃ māṣā iti saṅkhayāvattvaṃ dṛśyata iti
cet-satyam , tattu na ghaṭādisvarūpagatam, api tu
Similarly, since souls have no limits of space and time, there is no such emergent property for them such as Count.
... तादृशं तु सङ्खयावत्त्वमात्मनामभ्युपगच्छाम ।
... tādṛśaṃ tu saṅkhayāvattvamātmanāmabhyupagacchāma ।
In mathematical terms, the pūrvapakṣin is saying all countable sets are finite (since in everyday life all countable sets we see are also finite sets) and thus cardinality is a property of the set element itself. Rāmānuja disagrees and says it is possible to have sets that are countably infinite.