When I read the translation of that part, the first thing that came to my mind was "Oh ****, he's knows what Agasa's car looks like"
You know, along with him being suspicious about Sera phoning, Amuro may be remembering that on the highway, the car that supposedly belonged to Agasa was different than a yellow Beetle. So, in addition to his Sera suspicion, he has that look because he's wondering why the car is different than the one he saw. To be honest, at this point and with what's happened so far, I don't think it'd be a far cry to say that Amuro thinks Okiya is Agasa, since he paid most attention to him on the highway (and he doesn't really have many other names to attach to Okiya). Right now, Amuro has only heard of Agasa, that he's a guy that made a pretty useful gadget for a little kid and was involved in the chase. Since Okiya was driving and Okiya began to pull the 'shoot the tires from the car' trick - which Amuro noticed - it would be believable to say Amuro connected the dots in such a way that Okiya="Agasa". If I'm right about that, I think that when/if Amuro meets the real Agasa, his reaction will be pretty funny :X
As for Sera, Amuro obviously saw and noticed her on the highway, making the connection to Akai. If he was around to hear Sera questioning about Agasa's Beetle - not knowing that she was actually asking to go after Conan, not Agasa - he'd have even more reason to believe Okiya="Agasa". I'm guessing that Amuro has a sneaking suspicion that Okiya is Akai, so the thought of Sera asking about "Agasa" (in Amuro's case, Okiya/Akai) makes the sister/brother connection even more likely, even though he's off track.
...At least, that's what I've gathered at this point :X Obviously things could be different with more translation but as is, I think this theory is pretty solid.
and Ai is blushing lately whenever conan is beside her =) CUTE but not enough 
