That's certainly a hypothesis. What level of confidence should be required of that hypothesis before risking all of humanity on it? Who should get to evaluate that confidence level and make that decision?
One way of looking at this: If a million smart humans, thinking a million times faster, with access to all knowledge, were in this situation, could they break out? Are there any flaws in the chip they're running on? Will running code on the system emitting any interesting RF, and could nearby systems react to that RF in any useful fashion? Across all the code interacting with the system, would any possible single-bit error open up any avenues for exploit? Are other AI systems with similar/converged goals being used to design the systems interacting with this one? What's the output actually going to, because any form of analysis isn't equivalent to /dev/null, and may be exploitable.