It sounds like he has a problem with free will and omniscience, as well as a (less pronounced in this argument, at least) disagreement over what exactly is evil (and what evil is).
For the first: God created us with the ability to make real actual choices which, while able to be influenced, in the end depend on us.
That God knows what choices we will make “before” we make them does not change this - and I even put before in quotes because using time words like that with God tends to be problematic. God knows everything, all of creation (not only everywhere, but everywhen, past present and future) is visible to Him as a single object which He can view from the outside. God is not simply another creature who happened to stroll through time faster than we (or our perceptions or whatever) do and hence has seen everything already, but really and truly other and outside of creation.
I think that’s the key - there is no real conflict between God’s omniscience and the fact that our choices really are ours. The ability to make the choice comes from God, and He even knows which ones we will make. But the choice itself, that’s from us.
You could say that choice has its source in our ability to make choices which has its source in God so that the ultimate source of a choice is in God, but in this case “source” does not exactly mean “cause,” especially in any moral sense since the decision making ability we have, our person-hood, is not a clockwork thing following rules entirely built in by the source, but an actual real independent process which can come up with things independently of everything that came before it - to say otherwise would be to say you could blame a mother for the sins of her child because without her he would not exist. So again, key point: our choices are really ours, God knows what they will be, and God gave us the ability to make them, and there is no conflict between those statements.
Which leads into the second: And if our choices really are ours, then you can blame God for the possibility of evil, but not for each individual evil thing itself, since those originate in creatures. But while it is easy to argue that a good thing is better than a bad thing, it would be much harder to argue that the absolute impossibility of evil - with the limiting of will that that implies - is necessarily better than the possibility of evil. (Partially because an impossibility of evil removes the possibility of creatures being in any real sense able to do anything good as well.)
It is also worth noting that suffering (physical evil, or at least part of it sort of) and moral evil are distinct, and that both types of evil are more a lack or imperfection, or perhaps a perversion, a twisting, of good than things in themselves. Thus it is more that we in our obstinance are able to freely choose to not make things as good as we should make them rather than to create some other destructive force called evil which annihilates whatever goodness it comes into contact with.
With this in mind, the idea that we can say that the sentence “God is the source of the possibility of evil” (taken together with the idea that creation is moving towards perfection) can be rephrased as “God allows creation, seen at a particular point in time in isolation, to be less than perfect now so that it can participate in its own perfection and hence have some parts of it share in the good act of creation itself.”
That is to say, creation can not just refrain from containing those things we dislike and be devoid of suffering, but contain actual real good, actual people with the ability to do otherwise choosing to do what is right over self-interest and the like. Or to put it another way, creation as a whole (that is, considering all times rather than just all places, and not limited to the physical) really is “the best of all possible worlds” because there is very real good going on inside it which would not be there in a universe of automatons - but as a side effect slices of creation at specific times are less than perfect. (Or to put it in math nerd terms, a finite function can approach infinity without ever being infinite. In some ways I am too tired to explore at the moment, that actually seems like a pretty good analogy given that finite creation cannot be as good as the infinitely good God.)
An article related to the second part I recommend
patheos.com/Library/Roman-Catholicism/Beliefs/Suffering-and-the-Problem-of-Evil.html.
Caveat: there is a lot of 2am thinking at work here, so take this with a boulder of salt. But I think it mostly makes sense.
A non-creator God? Why not just be a naturalist? I would want him to clarify his position and why he thinks his god avoids the problem of evil.