You’ll note in the last paragraph that there is no really exact correspondence between Latin & English tenses. You’ll see in the example for the pluperfect that although “constiterat” would normally translate as “he had taken his position”, it could also be translated simply as “he stood”.
Additionally, participles are sometimes simply in a purely adjectival sense, which I suspect is the case here.
Participles are often used as Predicate Adjectives. As such they may be joined to the subject by esse or a copulative verb (see § 283):—
Gallia est dīvīsa (B. G. i. 1), Gaul is divided.
locus quī nunc saeptus est (Liv. i.8 ), the place which is now enclosed.
vidētis ut senectūs sit operōsa et semper agēns aliquid et mōliēns (Cat. M. 26), you see how busy old age is, always aiming and trying at something.
nēmō adhūc convenīre mē voluit cui fuerim occupātus (id. 32), nobody hitherto has [ever] wished to converse with me, to whom I have been “engaged.”
Allen, J. H., & Greenough, J. B. (1903). Allen and Greenough’s New Latin Grammar. (J. B. Greenough, G. L. Kittredge, A. A. Howard, & B. L. D’Ooge, Eds.) (p. 311). Boston: Ginn & Co.