Kara from Google announced in the Google My Business Help forums that they’ve updated how reviews work for hotels within the desktop search results.
“We’ve updated how Reviews look for hotels on Desktop Google Maps. Now, Desktop Google Maps displays reviews from both Google users and third-party providers (from TrustYou),” she said.
TrustYou is a third party hotel response software solution, so maybe they aggregate the data from Google?
With a consolidated list of reviews, users can make more informed decisions on Hotels directly from Maps. All hotels that work with one of the third-party providers are eligible for the unified hotel reviews section. A Google My Business account is not required. Please note that we cannot provide a full list of eligible third-party providers.
Forum discussion at Google My Business Help.