Undoubtedly he wrote the Sulbasutra to provide rules for religious rites and it would appear almost a certainty that Manava himself would be a Hindu priest.
The mathematics given in the Sulbasutras is there to enable accurate construction of altars needed for sacrifices.
Manava's Sulbasutra, like all the Sulbasutras, contained approximate constructions of circles from rectangles, and squares from circles, which can be thought of as giving approximate values of π.
There appear therefore different values of π throughout the Sulbasutra, essentially every construction involving circles leads to a different such approximation.
Gupta is concerned with an interpretation of verses 11.14 and 11.15 of Manava's work which give π = 25/8 = 3.125.