when my female basset naps beside me on the couch, rolls over on her back... and makes all manner of grunt noises until I scratch her belly.
my little chihuahua mix actually scoots his body over my hand to get a belly scratch.
Sounds like my house; within five minutes of jumping on the sofa, my basset is one her back, expecting a belly rub. My Chihuahuas spend a lot of time on our bed, to keep them away from the hound (who they detest, then again, they detest pretty much everyone except my wife). When you walk into the bedroom, the Chihuahuas quickly roll on their back and await THEIR belly rub
This research is just more “scientific” rubbish, pure and simple.