Intimacy cannot have a single definition. It is usually defined like one or more experiences of transcendence or intense emotion and touching hair is certainly one of them in my opinion, overlapping with concepts such as love, closeness, self-disclosure, support, bonding, attachment and sexuality.
Hair can be touched and played with in full view of one’s fellow humans in a way that other parts of the body cannot, and it is therefore used as a way of expressing repressed thoughts.
Intimacy usually denotes mutual vulnerability, openness, and sharing, but it’s still a broad concept that can vary based on the person experiencing it. The gesture of touching hair comes along with trust, consent and even security.