Here's why:
* Linking verbs connect the subject (velvet) to a word or phrase that describes or renames the subject (smooth as a cheek). They don't express an action.
* Helping verbs assist the main verb in a sentence. They help to form different tenses or moods.
In this case, "feels" connects the subject "velvet" to the description "smooth as a cheek," showing the quality of the velvet. It doesn't express an action the velvet is performing.