I think it could mean any one of the reasons you mentioned. The person could have wanted to reassure you, but sensed you didn't want to be touched or thought they might upset you, so they stopped themselves. Another reason might be that the person is in a professional job where they feel certain types of contact (hugs, touching the shoulder) shouldn't occur with patients. My first therapist was that way.

I think reassuring touches are therapeutic and it makes me feel the person cares when they initiate a friendly touch. Some people don't like to be touched.