This is quite unprovable of course, but I wonder if Herodotus’ choice of words was influenced by the alliteration at the beginning of 1.209:
Ἐπείτε δὲ ἐπεραιώθη τὸν Ἀράξεα, νυκτὸς ἐπελθούσης εἶδε ὄψιν εὕδων ἐν τῶν Μασσαγετέων τῇ χώρῃ τοιήνδε
The use of the device doesn’t seem to convey any particular intention or meaning, but maybe Hdt thought it sounds nice?
Compare 1.212 and see this thread Ending of Herodotus 1.
As a side note, it seems to me that usually Herodotus and Greek writing in general is not as adverse to repetition as English and doesn’t resort as often to synonyms to avoid it.