וַיִּרְאוּ֙ הַשֹּׁ֣מְרִ֔ים אִ֖ישׁ יוֹצֵ֣א מִן־הָעִ֑יר וַיֹּ֣אמְרוּ ל֗וֹ הַרְאֵ֤נוּ נָא֙ אֶת־מְב֣וֹא הָעִ֔יר וְעָשִׂ֥ינוּ עִמְּךָ֖ חָֽסֶד׃
their patrols saw someone leaving the town. They said to him, “Just show us how to get into the town, and we will treat you kindly.”
(The above rendering comes from the RJPS translation—an adaptation of the NJPS translation. Before accounting for this rendering, I will analyze the plain sense of the Hebrew term containing אִישׁ.)
The narrator is introducing a specific participant into the discourse while sketching a new situation. This is the prototypical setting for speakers to employ אִישׁ: to establish the situation in the audience’s mind, it is a participant’s essential involvement that matters, more than their attributes (such as age or gender).
As for rendering into English, nowadays the most natural way to call attention to someone of interest (in a newly depicted situation), especially with regard to seeing, is to use the indefinite pronoun someone, rather than NJPS a man.