First off he heads such a disagreement by capping conversation lengths: humans can't have infinite length conversations. Second of all: This is an assumption:

First off he heads such a disagreement by capping conversation lengths: humans can't have infinite length conversations. Second of all: This is an assumption: "The human does not. The human can run any program and produce a different output". A less charitable interpretation will also say this is wrong since it violates the Halting Problem. Essentially, you are assuming the human is some kind of hypercomputer.