The irony in Joyce's "Araby" goes deep beyond the bazaar itself. The narrator sees himself as a religious hero, and sees Mangan's sister as a Virgin Mary-like figure. As he courts her, so to speak, he is participating in a religious quest. Of course, this is an illusion.
The boy has not learned to separate the religious and the secular. The lateness of his uncle, the trivial conversation he overhears, the fact that the bazaar turns out to be a low-life place that sells low quality merchandise as a means for the church to make money, etc., lead him to the realization/epiphany that all has been an illusion.
He has been figuratively blind, as is the street he lives on (see the opening description of the neighborhood), and in his epiphany his eyes are opened. He understands that he has been silly, trivial, figuratively blind. He understands, it seems, that his relationship with Mangan's sister is not a holy crusade, and that he, in fact, has no relationship with her. He is not a crusader and she is not the Virgin Mary.
There are three types of irony: verbal irony, situational irony, and dramatic irony. Let's start with dramatic irony; dramatic irony is a type of irony that you encounter in dramatic productions - plays in particular, but also in TV shows or movies. Dramatic irony occurs when the audience knows something that the characters in the play or production don't know. Maybe you've watched a soap opera experienced this - you as the viewer know information that other characters don't, and you can't believe the silly choices they make based on this misinformation - that is dramatic irony. Do you as the reader have any knowledge that the boy doesn't about what will happen at the bazaar when you read this story? No, so it's not dramatic irony.
The next type of irony is verbal irony. You get this through dialogue. A person or character makes a comment that is the exact opposite of the intended meaning. This is something that we as humans do all the time. You're mother asks you to go to the store for her, and you are in the middle of doing something really important (English homework perhaps) and don't want to go at all, but you say, "Oh sure Mom, I'd love to." You've just used verbal irony (and in this case sarcasm too). The irony in "Araby" doesn't come from dialog, so it's not verbal irony.
The last type of irony to address is the type used in "Araby" in the scene you're asking about. It is situational irony. The boy is hopeful, believes that the bazaar will be exotic and magical, evocative and transporting, and that he will find just the thing to win the heart of the lovely Mangan's sister, but instead he finds the bazaar to be less than average, closing, lit by bright lights and full of rude people who don't care about him. The goods are common and are being put away. The disappointment he (and you as the reader) feels is caused by situational irony - the conflict between what the boy hoped to have happen and what actually happened when he got to the bazaar.