It says nothing to the point. And it doesn't make a whole lot of sense. Margaret was 170 or so when she died. Obviously Eb's plan worked. Eventually you grow up. and you can't blame everything that happens to you after that point on Mom and Dad.
I didn't say it was logical, and the parent's reasons may be perfectly sound. However that doesn't alter the child's sense of being abandoned and the anger of feeling unloved. Yes, Margaret lived that long, but was the quality of that life after she left Eb's teaching? Eb admits in Blood Rites that as her master he was too hard on her and in the end she rebelled. Can you imagine living your life happily for your first eleven or twelve years, suddenly this magical talent appears that you don't understand. Suddenly this man appears, claims to be your father and demanding the rights of a father and a master, being very strict and hard on you. Is it such a shock that she'd tell him to go fish? Or further that she'd extend that experience to the whole magical community who has the same values and go rogue? Maybe Malcolm was able to redeem her because he loved her and didn't ask anything of her but love. No, living a hundred and seventy years are great, but if they are mostly unhappy years spent on the hit lists of the Wardens, maybe not so much.
And nothing in the text prior to Jim writing that, said that Eb had anything to do with what happened to Harry after Malcolm's death. Jim pulled this out of his ass with no foundation. And the Morgan short story shows that Morgan believed Justin had done the deed. It never really mentions Eb at all.
But that is the whole point!
"Mom died when I was born," I said in monotone. "Dad when I was coming up on kindergarten. And you just let me alone."
Eb did nothing to locate his grandson. Harry languished in the foster care system for six long years before his talent began to show and Justin got a hold of him. Yeah, Eb may have barely managed to convince the White Council not to lop his sixteen year old head off.. But it may never had gotten to that point if Eb had stepped in sooner. Yes, out of guilt [he admits in Blood Rites, but he still doesn't tell Harry he is his grandfather] Eb tries not to make the same mistakes with young 16 year old Harry that he did with Margaret. However none of that mitigates the pain of those ten long years when Eb was no where around. Then when he actually gets young Harry, Eb continues to lie to him! Harry thought he was a god of integrity, it upset him to learn he was Blackstaff, and it was a few years more before he found out he was his grandfather.. Eb may have felt he was doing what was best, but that still doesn't change the anger and betrayal, logical or not that Harry feels upon learning the truth.
All things being equal, if I found myself related to Harry, I'd change my name, move to the Congo and hide in the deep jungle. Eb is a one man Death Squad who calls down comets and blows up volcano's, with no more of a rationale than he believes it to be the right thing to do. Margaret has murdered with magic, conspired with the Black Council or was at the minimum a fellow traveler, who abandoned one child and arranged the birth of another to create a weapon.
Harry is still owed the truth, and no matter how bad, it is better he knows the truth and learns to live with it, than be lied to. Harry's instinct was to avoid his daughter forever out of guilt. Murphy and Michael talked him out of that, the hard part will come when he has to tell her how her mother died. Chances are she already knows, she was there.
As for Harry, if I was a women I wouldn't get around him without an asbestos suit, body armor and a steel neck protector. He makes deals with no intention of keeping them. And has a brother who is a serial killer. He runs a Super Max prison and pisses off everybody at one time or another because he can't shut up.
Are you saying Murphy is a stupid woman? Or how about Susan, they soul gazed and she fainted. All you say is true, but in his heart, Harry is a good man, remains a good man, ask Michael.
This is what really shows the Jim is a rare writer, he makes Harry and his friends lovable. 
And why not? He isn't a monster, he tries to do the right thing, it may not always work out, but he tries.
No but you can tell them how damaging their choices were when they start telling you how to raise your child.
Sound advice for grandparents everywhere, even if you did a good job, never give unsolicited advice to your kids on how to raise their own children. You won't get the appreciation you expected, more than likely, good or not your advice will be resented.
