In short, I can't see anything that would explain any change in Google News behaviour based on whether `googlebot-news` is or isn't in that list - because it'd use the googlebot entry.
Considerations
• If googlebot-news were anywhere else in the robots.txt file, there could be some conflicts / issues with adding it here
• As mentioned upthread, googlebot-news isn't actually a crawler, so the effect would at most be on inclusion in news, and not seen in crawling activity
Thanks for indulging my trip down a rabbit hole, and sorry I can't solve the mystery