Actually,

I'm going to explain this fully here and now just so it's out there.

Before the fight even took place:

All of the talking Johnson did was just to hype the fight up.
I doubt that he seriously believes what he says for this hype. It's just a show.
I am pretty sure he knew he would not win.
Whatever his reason for taking the fight... we may never know, but I'm pretty sure he knew the deal.

Now, after the fight, since he is not retiring soon, he will obviously have more fights - therefore - he must generate interest.
Hence, the hype that you are seeing now from his page.
It is just 1 method (as there are many ways) to generate attention.

When you see this sort of thing, keep that in mind. Many boxers do this.
Talking bigger than they are. This is not new. Not all boxers use this but some do. It's not new.