Sensation, it appears, is literally touch: atoms touching the human body. That seems to serve for sensation, thought, memory, etc.
Is that what you're getting?
Yes I am looking for further ways to explain how they would have seen the term "pleasure" to cover everything that is not painful. If you view every sensation involving awareness of smoothness as sort of an ultimate-level explanation, the "touch" that is involved in all sensation might have been seen as the mechanism. Maybe this was a way they might have explained the nature of pleasure as a touch sensation regardless of whether the touching that is involved comes through stimulation or through regular functioning.