This is difficult to pinpoint why Rizwan started the conversation without any greeting. But it can be attributed to several factors like the thoughts going on in his mind just before the man appears, the sense of urgency lest the man be gone without stopping, and the normalcy of starting a talk among common people without introduction in the third world countries.
 
Regarding the character trait of Rizwan, I don’t really think that this indicates any or even the writer meant anything significant here. You may be wanting to hear things like his rudeness, uncivilised manners or something in line with that. But, I feel the conversation beginning without an introduction was rather due to a sense of urgency as everyone was busy in the crowded marketplace to earn his own bread. At most, his troubled mind due to unemployment and poverty can be mentioned here.