Note Zodiac says "The way I stated I would" which to Me seems like He's admitting the way He said it, ie, to take on a school bus, was never to be taken at face value but was simply a masked threat toward a school Kid rather than School Kids. The School Kid I believe He'd threatening is the witness referenced in the FBI report, a witness the report declares: "Eight year old witness in murder of Taxi driver Identified (Xenophon) Anthony as Possible subject in this matter." Zodiac, in a subsequent letter, chins authorities for taking His threat as literal and at face value saying: "If You cops think I am gong to take on a school bus the way I stated I would, You deserve to have holes in Your heads."
If this is a masked threat toward the eight year old witness who Identified Zodiac, then it suggests that Xenophon's ID by this witness was accurate and that Xenophon Anthony is The Zodiac because if Zodiac knew that A witness had identified an innocent person as being possibly responsible, then He'd have no need to threaten the witness and would likely be in His own favor to allow the authorities to believe the witness knowing He had ID'd the wrong person. The fact that Zodiac threatens school children, or what I believe is a specific school kid, suggests that the school kid had in all probability ID'd the correct suspect which is why the suspect responded by threatening Him to keep His mouth shut.
Let's also not forget, The Zodiac has been seen by cops on October 11 and, quite obviously, Zodiac knows He's been seen and according to Zodiac Himself, backed up by first responding Officer on scene, Armond Pelissetti, Officers Fouke & Zelms actually stopped Him and spoke to Him "Face to Face." With this in mind, it makes little to no sense for Zodiac now, knowing He'd been seen and spoken to by Don and Eric, to fire off a letter a day later announcing that He, The Zodiac, was responsible for this crime because in doing so He surely knows that Police will now know what Zodiac looks like. Why drop such evidence in police laps when keeping quiet would mean Law Enforcement would be none the wiser to this crime actually being one of His? If He just kept quiet then Paul's murder would forever be a cab robbery gone wrong and nobody would have any cause nor reason to attribute this crime to Zodiac. But, for some reason, Zodiac writes the letter anyway knowing it will mean Cops now know what He looks like and there has to be some method in His madness here and I think He had to write it because He wanted to instill fear in the Kid who ID'd Him by revealing that He Hasn't ID'd just any petty criminal here, but, in fact, the man He's dealing with is actually the ruthless, cold blooded and infamous, Zodiac!