[Someone]

I think the claim is bogus not because the brain has a much more complex instruction set, but because the phrase 'instruction set of the brain' does not make sense.

If one had to express the complexity of a neuron in the size of its 'instruction set', the best guess may be 'one': "act like a neuron until you break down".

The complexity of the brain most likely is not caused by complexity of the processing units, but of its parallelism.