This is very simple. If you are not alleging that Brewer was acting for nefarious reasons, then what is the purpose of questioning his motives for finding Oswald suspicious? Even if you believe his suspicion was unfounded, why does it matter? If Brewer thought Oswald was acting suspiciously (even if he was not) it doesn't change the narrative one iota. Brewer believed - rightly or wrongly - that Oswald was suspicious and that ultimately led to the chain of events resulting in his arrest. So what?