As linked from the site you provided in the question, the Political Wire reports reports that the author of a promotional booklet that included a brief erroneous bio of Obama has explained:

You're undoubtedly aware of the brouhaha stirred up by Breitbart about the erroneous statement in a client list Acton & Dystel published in 1991 (for circulation within the publishing industry only) that Barack Obama was born in Kenya. This was nothing more than a fact checking error by me -- an agency assistant at the time. There was never any information given to us by Obama in any of his correspondence or other communications suggesting in any way that he was born in Kenya and not Hawaii. I hope you can communicate to your readers that this was a simple mistake and nothing more.

Note: This was a promotional booklet for his then-literary agent, Acton & Dystel. It is not part of his book of memoirs.

As linked from the site you provided in the question, the Political Wire reports that the author of a promotional booklet that included a brief erroneous bio of Obama has explained:

You're undoubtedly aware of the brouhaha stirred up by Breitbart about the erroneous statement in a client list Acton & Dystel published in 1991 (for circulation within the publishing industry only) that Barack Obama was born in Kenya. This was nothing more than a fact checking error by me -- an agency assistant at the time. There was never any information given to us by Obama in any of his correspondence or other communications suggesting in any way that he was born in Kenya and not Hawaii. I hope you can communicate to your readers that this was a simple mistake and nothing more.

Note: This was a promotional booklet for his then-literary agent, Acton & Dystel. It is not part of his book of memoirs.