Since John's cultivation was crippled, Lex had no idea if he could communicate with the soul inside of the dragon's body, so Lex arrived on scene as himself. At the same time, it would not hurt to show John the kind of problems he himself had gone through. Though to be fair, Lex did not doubt that John would have been able to face any other issue without any hesitation.
But his entire identity was built based on his system, which is what was causing him to freeze. Lex did not blame him or think little of him. Often it is said that those of older generations have a hard time learning new things. John had already lived so much of life, but had no idea how to live without his system, which was causing him to freeze. But a kick start to show him it would be okay should help him overcome that hurdle.
