Obviously, the state not allowing itself to intervene is obviously not an exercise of the power of the state - it's an exercise in restraint of said power.
Obviously, that's just semantics - one could just as easily frame it as "the state is using it's power to make it more difficult for individuals to seek redress against corporations that discriminate against them." No matter how you look at it, the state is using its power to make discrimination easier.
The actual discriminatory power in this case comes from the individuals and corporations that discriminate - if there are none willing to do so, or if there are few enough and their scale is small, then it's all of no consequence. Even if said discrimination is pervasive, it is still limited to what private entities can legally do - so it's a very far cry from what government-powered discrimination can do (for example, it is not legal for corporations in the USA to summarily round up their customers and murder them in gas chambers; or to incarcerate them because they married a person of a different race).
So what? So because the corporations can't round up people and execute them, that makes this law okay? Your argument boils down to "well, at least Indiana isn't making it legal for corporations to start KILLING gay people, so we should be happy that they're only making it easier to discriminate against gay people."