China Eastern started offering free transit hotels to passengers this year. To be eligible, the basic rule is that you are transiting and there are no more flights to your destination on the same date.
“passengers who purchase ticket from our Hong Kong official website and need to transit at Shanghai, Kunming and Xi’an, connecting domestic or international flights on the next day due no same day connection flights, passengers may enjoy one night complimentary transit hotel accommodation service!”
China Eastern’s website is fairly thorough in explaining the process in English, so I won’t reiterate. I like this move as most airlines are getting cheaper, MU is offering an additional amenity. All of the hotels are rated 3* so don’t expect luxury, but I wouldn’t expect them to be clean and sufficient for an overnight stay.