James Patterson Writing Style

I've read a few dozen of his books. They're all written in American English, as one would expect. But I've just come across one written in British English. Language, spelling, idioms, everything, The title is Private Games, one of the Private series. It takes place in London, the 2012 Olympic Games. There is anther book in the series, Private London, also in London, where British characters use British terms, like "mobile" for cellphone, but it's written in American English. I found the style used in Private Games annoying. Why would he do that? Ideas? Opinions?

 

James Patterson doesnt write all of his books.
The author who wrote Private London (Mark Pearson) is British

 

I was talking about Private Games, co-author Mark Sullivan, an American.

 

Possibly he has dual citizenship, or just has lived in both countries?

 

He may have gotten the commission for Private Games, which was a detective book based in London with a british investigator, and began writing in character.
Writers do that. Good writers can do it well.

 

Private London, if im not mistaken, starts in the US with an American protag before going to London.
That would explain why its in American English but still has british isms in it