When the current daylight savings schedule went into effect in 2007, the news articles at the time included a cautionary warning that your computer might not automatically make the change if the operating system was configured to the old schedule. Then newer your system, the more likely the new dates were already programmed in, and you would be fine.
So its possible that an old server somewhere in the Disney universe was still running with an outdated DST setting, and no one knew about it. I would agree that it is quite improbable that this could happen for a company as invested in customer-facing technology as Disney, but it would explain the goof up.