Even if Ciel weren't completely entitled to shove Sebastian's hands as he pleases, Sebastian hardly has the strength right now to put up any resistance to it. Not that he tries: he just looks confused.]
I'm sorry? [What did he do now? There's just no pleasing the young master today.]
You... will need to clean up, however. [Ciel is dirty --> Sebastian should draw a bath for him --> Sebastian will need to undress him and help him bathe --> all of that requires touching.
Very sense-making, if only he'd articulate the entirety of that thought process.]