Also the patent application claims priority to a provisional patent application filed October 24, 2014, which was in all likelihood filed in view of the paper being submitted on October 30, 2014.
Okay, that would allow it - the gap is slightly (1 week) less than a year, and the paper is published by Google employees who presumably are in the patent; the publication would still disallow someone else from patenting it even within that one year.
If memory serves, Google did this with Word2Vec as well, which is a bit sketchy.
If you open source something, there should be a reasonable expectation that it is contributed to the commons. Otherwise a lot of people will build off your stuff, which you can then turn around, file a patent, and claim infringement.