No, that's not proof. Being unable to answer an illogical question isn't a failing of logic, it's a failing of the question. The rsponsibility of logic here is to show that the question is illogical, and when we discuss an illogical question, by definition logic has succeeded in showing that it is an illogical question.
The question is only ridiculous is omnipotence itself is a flawed concept. If omnipotence was not flawed, then it could stand up against this question. This question demonstrates that an omnipotent being is logically impossible by showing that, being omnipotent, it can create anything that is not internally logically contradictory, and there is no internal logical contradiction to a rock being heavy, or, to avoid semantics, a bar of metal being difficult to bend. It's only when you introduce omnipotence into the equation that the problem arises, meaning that omnipotence is itself a flawed concept.
By providing an example of something which contradicts currently known logic.
I left the rest in not to take it out of context, but that right there basically tells me it's a bad question. After that it sort of gets redundant because you try to explain why it's a bad question, but there could be other reasons as well that don't support your point as to why it would be a bad question.
I'll tell you why it's a bad question, and it has nothing to do with god, it has to do with the idea of anything being infinite which is what creates the paradox.
It's a question that goes off the basis that the paradox is presenting is true. presents something as being possible that under earthly circumstances would never be possible, and asks whether or not it's possible, which the obvious choice is "no"... it's a loaded, and therefore shitty question.
Ultimately, and this will probably be my final argument... Whether or not god could create something so large he could not lift is irrelevant. It certainly doesn't disprove god's existence because whether there is a limit or not to what a god is capable of is irrelevant.
Even if holy texts say "god can do whatever he wants whenever no matter how illogical" doesn't necessarily make that the case. If you look at anything logically, there is almost always a limit. It's obvious that wherever that limit lies, if in fact it exists, it's so far out of our reality it's unfair for us to even speculate about.
See what I'm getting at?
So even if it proves that god isn't all powerful, so what? It has nothing to do with god's existence.
edit: and it doesn't really even prove that either. All it proves is that humans can come up with clever paradoxes to confuse people. =)