That is only partially accurate. Lamon's name actually appears on two different biographies of Lincoln, one of them ghost written and the other his own.
The first biography was published in 1872 and did indeed rely heavily upon a ghost writer he hired, Chauncey Black. Lamon contracted the book out to Black, though he did provide virtually all of its source material in the form of personal papers and a loaned collection of letters and interviews accumulated by William Herndon for his own biography of Lincoln some years later. Black's first version came across as overly negative towards Lincoln and prompted David Davis to advise that Lamon make a revision. Lamon did just that, toning down the material substantially though still portraying a less than saintly Lincoln. Though some parts of the 1872 book are still questionable, Lamon spent a great deal of time in the mid 1870's writing and publishing his own defenses of the book when some of the unflattering anecdotes were challenged.
The second Lamon book is given substantially greater and in fact practically universal acclaim by historians. Lamon himself wrote it, largely at the urging of Lincoln's former Secretary of the Interior after the two conversed upon the fact that they were among the last living members of Lincoln's "inner circle." Unfortunately it was still incomplete at the time of Lamon's death so the timeline between each of the essays is very fragmentary. Lamon's daughter had the portions that were completed published around the turn of the century following her father's death. It is from this second Lamon book that historians get some of the most famous Lincoln anecdotes such as the warnings he received not to go to Ford's theater and the midnight pass through Baltimore before the inauguration.
So which book does the Taney arrest story come from?