Is there reason to believe the brain is chaotic on that level? The reason I doubt it because any stable biological system has as one of its primary tasks - if not its #1 primary task - to maintain equilibrium. Otherwise it would collapse into chaos due to the inherent imprecision of molecular phenomena. So I would be very surprised if you could stimulate a neuron - not even a neuron, but an electron inside a neuron - and cause something as complex as an idea to form. More likely it would be equilibrated away
That said, just saying "chaos theory means any change can cause anything" is a terribly weak argument for "cosmic rays cause ideas". Not to mention all the reasons why it's implausible as a significant idea generator.
