But I assume the title is a bit catchy.
Or are you considering the process of downloading the videos from YouTube hacking since it's against their terms of service?
The idea of 'hacking' you are referring to is a colloquialism that is shared by young teens and entertainment media. It is not a reflection of reality.
"A hacker is a person skilled in information technology who uses their technical knowledge to achieve a goal or overcome an obstacle, within a computerized system by non-standard means."
There was a time, not so long ago, security bugs hunters would claim they found some oddities within a sub module of some software, then disclose how it leads to escalation of privileges, 7 other severe flaws leading to remote code execution, ending with a mention that it makes half of the internet vulnerable since it's Apache or some other broadly used utility.
I guess parsing an MP4 file from YouTube is now classified as "hacking YouTube".