Don't do what the guy in the video did, that's weird to just touch someone like that. But if you strike up a convo with a woman about their hair, compliment than and give off a safe and chill vibe, asking is fine. You have to strike up a conversation with them first though so they can see you're not a creeper.

Many, many woman with hair this long do not wear it down like this unless they want people to notice them for it. So...notice them! Just respect their boundaries.