وَجَاءَ رَجُلٌ مِنْ أَقْصَى الْمَدِينَةِ يَسْعَى
A man came running from the farthest end of the city. (al-Qaṣaṣ 28:20)
“رَجُلٌ” is indefinite. The verse reports the arrival of a man without making his proper name the immediate point. Attention falls on his coming and the manner of that action rather than on a named identity.
Indefiniteness can present one member of a class. It does not necessarily mean that the speaker does not know who the individual is; the form may simply serve a different communicative purpose.