The Google News & Weather app for iOS was updated on Tuesday both with "performance enhancements and stability improvements" and support for Apple Watch. I haven't seen any other Google apps ready for the watch, so this appears to be the first.
Like most other watch apps for Apple's wearable device, Google News & Weather for the watch is essentially an extension for the iOS app. You can't have the watch app without installing the software on your iPhone, that is. Google included the ability to add News & Weather to your Apple Watch glances for quick access.
That's because the watch requests data on demand from your iPhone over a Bluetooth connection. It's no worse than other apps, but it can be annoying.
While it may seem odd for Google to put its own apps on the Apple Watch when the company has its own smartwatch platform in Android Wear, I don't think it is.
Google has long supported iOS with nearly all of its apps and services, save for a few: I'm looking at you Google Keep.
Google also doesn't want to miss out on getting user data from iPhone owners, since it uses that information for its advertising business. By skipping support for the Apple Watch, Google would potentially lose out on some of that data.