Get earning from YouTube is not a passive income because you have to make a video creative to be able to make people interested in watching your videos and it needs to be done on a regular basis with new ideas every time you want to make a video so obviously isn't passive income.
I still think its passive because when you're done creating a quality video you can leave it and see your earnings if you have plenty of subscribers . I dont think of any passive income that requires no action you have to work on it first then the passive income will come.
To my point of view I don't agree that youtube is passive income in the sense that "passive" means do nothing but you always have a source of income. Assuming that someone is doing his first video and many people subscribe it and at first earns some money of it. Do you believe that next years of his life he continues to earn money? Of course not; because his subscribers will already have seen that video and if he is not talented to keep them, that is to make a new and better than previous one, they will leave, unsubscribe and views per day will go to zero that is zero earnings.
Youtube monetization can be a passive income. For example, you regularly post lectures online just to teach kids about a certain subject. You didn't intentionally uploaded those videos to make money. When you start monetizing your videos, that becomes a passive income since basically you're getting paid for something that you would always do but it's not like a job.
Not everyone that's posting on Youtube is doing it solely for the purpose of making money. Although the percentage of Youtubers doing that is starting to blow up.
It may be youtube, blog or vlog, social media like facebook or forums on various topics would help in earning money without actually working actively on it. The 'Passive income' tag would go away when person considers focusing on social media for primary income only. Many youtubers have made it their profession.
Apart from youtube, there are people who have started groups on facebook or similar social media groups and they are earning based on membership of that group. For example, a person has started an 'eatout group' for specific city. This group initially focused on reviewing and getting honest reviews of people/members of group who visited those hotels/food-joints/places. As membership of group slowly exploded then admin of page/group started making money by selling coupons for some hotels. Admin then employed other subadmins to look after the page, so that other people do the work for him.
Another example is, a person started a business of security camera. Business is done from home, he would hire only needy freshers who are desperate for job experience. That is first preference is get experience certificate rather than earn money. This experience is to show at next better job interview. One group of fresher would get new customers/orders while other fresher would do the work of camera installation and configuration. Also collect the payment from the customer. There employees would use their own vehicles/cars to reach customer. Owner had different business as his main line of earning altogether. This camera business was earning him very handsome (million per year) income.
One good example of passive income is lending car to commute/travel companies. If you purchase a car for that purpose only and strike a deal with companies like Uber or any local company (who work with Hotels/motels) then they will take care care for 2year/4year and will give specific amount monthly.
https://yourstory.com/2014/04/barber-rolls-royce-ramesh-babu/Again it is not only the idea however ability execute that idea without your full time involvement.