I only quickly browsed the sutta (not reading it all) but the question seems to not really be relevant to the Buddha because it was not the Buddha that introduces the phrase: "development of the body". Instead, it was Saccaka the Jain that introduced the phrase, probably from Jainism.
Then Saccaka the Nigantha...said to the Blessed One, "There are, Master Gotama, some brahmans & contemplatives who live committed to
the development of the body..."
The Buddha answered as follows, which is just the standard teaching about development of mindfulness & wisdom in relation to the six spheres of sense contact:
And how is one developed in body and developed in mind? There is the case where a pleasant feeling arises in a well-educated disciple of
the noble ones. On being touched by the pleasant feeling, he doesn't
become impassioned with pleasure, and is not reduced to being
impassioned with pleasure. His pleasant feeling ceases. With the
cessation of the pleasant feeling there arises a painful feeling. On
being touched with the painful feeling, he doesn't sorrow, grieve, or
lament, beat his breast or becomes distraught. When that pleasant
feeling had arisen in him, it didn't invade his mind and remain
because of his development of the body. When that painful feeling had
arisen in him, it didn't invade his mind and remain because of his
development of the mind. This is how one is developed in body and
developed in mind."
When suttas are read, such the often cited SN 44.10 which is about 'self' & 'no-self' (rather than about the Buddha's doctrine of 'not-self'), I suggest we should be very careful about putting words into the Buddha's mouth based on terms used in questions made by non-Buddhists.
Another example is the Tevijja Sutta, in which the Buddha answers questions to Brahmans, yet some scholars believe it is about Nibbana.
Asked about the path to union with Brahma, the Buddha explains it in terms of the Buddhist path, but ending with the four brahmaviharas;
the abbreviated way the text is written out makes it unclear how much
of the path comes before this; Robert Gombrich has argued that the
Buddha was meaning union with Brahma as synonymous with nirvana.
Similarly, the Buddha often uses the term 'nama-rupa' in answers to questions made by Brahmans. Since the Brahmans did not know the Buddha's teachings, the term 'nama-rupa' in these contexts probably retains the Brahmanistic meaning.