No, you're as wrong as he is about blackmail. The links you cite show that.
There is no coercion. Your first wikipedia link says "[c]oercion involves compelling a party to act in an involuntary manner by the use of threats." Saying, effectively, "I no longer wish to be associated with you" is not a threat.
It's also not extortion. Your second link says "[e]xtortion is the practice of obtaining benefit (e.g., money or goods) through coercion."
Again, there is no coercion, and advertisers choosing not to advertise on his platform are not "attempting to gain benefit" at all. They are trying to avoid what they perceive as harm to themselves.
He is not "off by a hair," and neither are you. You're both miles away from even being able to see the ballpark.
> "I no longer wish to be associated with you" is not a threat.
Some people take this as a threat, because they believe they have a right to force you to listen to their opinions. To my eye, this belief is what caused Musk to buy Twitter in the first place. I think it’s breaking his brain that he still can’t get what he wants out of Twitter after spending $44 billion on it and reshaping it in his image. Must be tough.
If somebody walks past a shop and does not buy the wares on offer because they are offended by the horrible decor, I assume, under this definition, this will be called coercion in that that they 'coercing' the owner to change the decor?
It is compelling him to behave in an involuntary manner, thus coercion.
https://en.wikipedia.org/wiki/Coercion
Advertisers are attempting to gain benefit via coercion, so it is extortion.
https://en.wikipedia.org/wiki/Extortion
So far as we know, they are not threatening to air secrets, so it is not blackmail.
https://en.wikipedia.org/wiki/Blackmail
So it was a bad choice of language, but frankly it doesn't seem "incoherent," just off by a hair.
It also does not seem petulant, though telling advertisers to F themselves through that sneer of his certainly is.
> he keeps saying and promoting repulsive stuff
Yes, and the responses to him seem repulsive, too. Chicken? Egg? I don't care.