Update: this is a hotel-specific snippet as confirmed in this Google Business Support article. However, the use may expanded in the future depending on the review sources that Google taps into.
Spotted today on a branded search for a hotel, there’s been a lot of changes recently with the Google+ updates and removing their influence from the actual Google+ page. However, it looks like more changes are coming as Google is now more prominently showing review summaries. This particular hotel has about 80 Google+ reviews at the moment, higher than the average local or smaller business. This may be contributing to the ability to pull different snippets from the review copy and show it here in the knowledge graph. My gut tells me that reviewing on Google and the seemingly phased-out Google+ should be getting easier as they show off these reviews more prominently in search and companies’ knowledge graph snippets.