BIlbo was well aware of Thorin's not being a very physical person. Whether with friends or his kin, he was the same. Which was why his hand only lingered briefly on the Dwarf's shoulder. He never wanted to make his friend uncomfortable. He had a great deal of respect for him, and making him uncomfortable was the last thing he wanted to do.
Seeing as they had yet to find half pints here in Madison Valley, and Bilbo didn't particularly care to drink ale from anything other than a pint (or half pint) glass, he often only filled the pint glass halfway. He knew his limits, and while he knew he could drink more than half a pint, he often didn't.
Except for today, apparently, because he filled his glass up before passing the ale to Thorin. "I was told that if we do not care for a particular flavor, there ay many others to try, that we shouldn't give up."