Why does the officer think the man should notice the speed limit? [originaltext]

W: Can I see your license and registration please?
M: What’s the matter, officer? Did I do something wrong?
W: You were speeding.
M: I was speeding?
W: You certainly were. Do you have any idea how fast you were going?
M: I’m not sure, but I would think I was going about 35.
W: This street is in a 25-mile-per-hour speed zone, you know.
M: It is?
W: In this state, the speed limit in residential areas is 25 unless otherwise posted.(4)Besides, there are signs all along the streets.
M:(5)I’m sorry, officer, I guess I didn’t notice. I was thinking about my job interview. I’m on my way to it right now and I hadn’t planned to come this way.
W: What do you mean?
M: Well. I was coming down on Elm Street but the traffic was really backed up. There was some kind of construction going on. I turned onto a side street and ended up here. Give me a break. I’m nervous enough as it is.
W:(6)Well, since you have an interview, I’ll give you a warning this time. But keep your eye on the speedometer from now on, whether you’re on a street you are familiar with or not.