This isn't the first time that you've been able to get Lightroom in the Mac App Store. Back in 2012, when Adobe sold its apps as standalone purchases before starting to push Creative Cloud subscriptions, Lightroom 4 was available for $149.99. Lightroom 5 never came to Apple's store, however, and even Adobe itself doesn't sell standalone versions of Lightroom today.
This news means that Apple has landed another major app on the Mac App Store, which has faced many years of criticism and will generate revenue from its split on in-app purchases. Lightroom CC is still available outside of the Mac App Store at the same price, but will not have as streamline of an update process.