Your point of view has everything to do with it. If this was a visual medium Jim could do it another way, but if he doesn't put a label on it, it loses its punch. So wizard and he who walks behind makes sense. Anything else doesn't. The assumption Jim hands you is that the sight interpreted what he saw, for him.
Huh? You are not making any sense... Let's read the quote again shall we? 134-135 Storm Front
The young man looked at me, and his eyes rounded and dialated, until I thought they had turned into huge black coins dotted with his bloodshot eyeballs. Hiseyes rolled back into his head until he could hardly have been able to see, and he started to shout in a clarion voice
It is the kid strung out on Three Eye looking at Harry.. Harry isn't using his wizard sight, he isn't interpreting anything.. He is just startled by this kid looking at him and now shouting at him...
"Wizard!" he trumpeted. "Wizard! I see you! I see you wizard!
That is the kid recognizing Harry for what he is, though how would he know a wizard when he saw him? How would he know a wizard from someone else with a magical aura? The kid yelling at Harry, "Wizard!" Vocal, no interrelation needed from Harry or us...
Next line, this is the strung out kid further telling Harry.
"I see you wizard! I see the things that follow, those that walk before and He Who Walks Behind! They come, they come for you!"
It's the kid who sees Harry not only as a wizard, but that he was mixed up with the likes of He Who Walks Behind. Not only would this kid not know a wizard on sight, but how in the hell would know an Outsider if he saw one? Let alone his name?
Harry goes on to say lower down on page 136 that he is marked by his encounter with Outsiders, he goes on to say
But only a wizard had had that kind of vision, the ability to sense the auras and manifestations of magical phenomena. And that junkie was no wizard.
That is the mystery, not just that Three Eye is real, it enabled the kid to see auras and magical phenomena, but it still doesn't explain how he'd know that Harry was a wizard or HWWB by name.
If you reread his shout out to Harry, "I see you wizard!" I get the feeling that the kid was sending
a message to Harry from someone.. The kid was somehow taught what to say if he ran into Harry a head of time, someone who knew the very mention of HWWB would freak Harry out, which it did a bit... Then the question becomes, who taught him?