The difference between lying and joking is always in context. If I dress as a police officer for Halloween it's fine, if I lead you to believe I actually am a police officer it is a crime. There's also a middle ground where someone could mistake my costume for impersonation.
I don't know what aspect of this video violated the terms of service, but I think political videos on all sides regularly make statements that aren't supported by 'mainstream' fact checking sources and therefore might fall outside the policies of services like Youtube.
If you want to argue that all speech with 'political intent' should be protected I am open to that conversation! But that is not the standard held by most services, including Youtube, which Bryson Gray agreed to when he uploaded his song.
One type of humor is known as "trolling". The basic idea is to see how much of a reaction you can get from something pointless and stupid. Now many people are making songs with the lyric "Let's go Brandon" and they are receiving hate mail, being banned, being demonitized, etc. This reaction is seen as outsized for a reference to a fairly well known piece of pop culture. Thus, to those who find outsized reactions funny, this is funny.