Celebrity plagiarizers always give the same excuse, always

"The mistake, he said, occurred when he confused the notes he had taken about Ms. Lepore’s article — he said he often writes his research in longhand — with notes taken from “Gunfight: The Battle Over the Right to Bear Arms in America,” by Adam Winkler (W.W. Norton, 2011), a copy of which was on his desk at his CNN office."  And how could one confuse his/her own words with someone's else?  I never understood that.  I mean, when he was copying the words from the ostensible longhand notebook, he was not able to know that these are not his words?  I mean, I never confuse my words with those of Hegel, for potato's sake.