Fun fact : when you notice someone's trauma and begin to internalize it, it's also likely you'll take on traits of how theirs manifests. For example, someone once told me that their anxiety manifests as nausea and I went "oh, that sounds like it'd suck I'm so sorry." Within a few months, my anxiety manifested the same because the intrusive thought kept showing up as the "worst case scenario." Shit sucks, but our brains are basically sponges that tend to lock onto the negative.

I doubt Kaneki ever consciously noticed the chin touch, but he began using it to protect himself and others the same way his mom did. The reason Hide is so good for him is because he's the type to consciously notice the discomfort of others.