Hopefully this will help,
"...Next, the erudite may make a Psicraft check (DC15+ power's level) to see if he understands one of the powers. If the power is not on his class list or is a discipline power, he automatically fails this check."
I do believe what we have here is a dangling modifier. This is just written poorly, with the correct inflection it makes sense. I believe the following is what he intended:
If the power is not on his class list or is NOT a discipline power, he automatically fails this check.
What does this mean? It means that powers that are reserved soley for psychic warriors(or psychic thieves) are out, psion/wilder powers + discipline powers are in. I think the 'not' in the articles wording was meant to apply to both the list and discipline powers... perhaps the 'is' before 'a discipline power' is a typo... if you remove it it makes perfect sense when spoken aloud. Either way... discipline powers were meant to be included