invincibility means you cant be hurt, you cant be killed, your complitely invulnerable regardless. your also incapable of being conquered, defeated or subdutied. sounds like omnipotence to me.You must be registered for see images
The writer states his invincibility, not omnipotent.
More credibility to mine is that it is the entire manga page, not just a snipet like yours is.
Lastly, Buu thinks he has just beaten everyone so of course he will say things like that. He thinks he is the strongest person there is, which at that point in time was true.