I had no intent of linking to the book, I was even uneasy mentioning it.
It does however relate in that the President has 1 known incident and may have others which we haven't been told of. In general people running for public office don't go into details about their past misdeeds from before they were adults if no legal actions were ever taken.
As to the Romney matter, he may be in even worse shape if it turns out he is now lying. I say this because John Lauber's family is questioning the accuracy.
Whoa: Family of Romneys Alleged Bullying Victim Says Story Inaccurate, Theyre Disgusted by WaPo | The American Pundit
The family never said the incident didn't happen, just that the story is inaccurate. Nowhere does it mention how the story is inaccurate.
I will say that the website you got the story from seemed really unbiased though.