Couldn't and shouldn't are two different things. Maybe Joe could have interjected himself more into the matter, but that doesn't mean he should have.
To your point, it's clear from the notes and emails from that time that C/S/S did not believe they were dealing with CSA. They were, however, trying to prevent the kind of he said/he said scenario that occurred in '98. Why else would Spanier have written, "The only downside for us is if our message is not “heard” and acted upon, and we then become vulnerable for not having reported it."? If they were dealing with a case of abuse, what Sandusky did or did not do in the future, would have had no bearing on their vulnerability. IOW, they would have been vulnerable anyway. The boy could have come forward at any time. Had he been abused, he would have been the topic of their discussions. That he was not even mentioned in their notes and emails speaks volumes.
Because Spanier and the others believed they were not vulnerable, so long as Sandusky adhered to the restrictions they had placed on him, it is obvious that what they believed they were dealing with did not rise to the level of CSA.
Jack Raykovitz, however, had a legal and moral obligation to report.