That's not what I want to know. I wondered how his brain would react.
His brain will react to information based on how the pizzas were presented to him. In the case that he was told 'there is pizza 1 and pizza 2 which one do you want?' his brain would likely react most the numbers assigned to the pizzas. In the case that the pizzas were put in front of him one at a time and he was just asked 'this one' or 'this one', then he would react largely to the sequential order that the pizzas were presented.
There will always be information presented to him which differentiates the pizza, and if there isn't he won't be able to indicate a choice. For example if no information was provided a conversation would go like this:
"Pick a pizza"
'wut, what pizza?'
"we have pizzas just pick one!"
'erm ok I'll whichever one you think is best'
"no, you have to pick"
'I don't care, just give me whatever I have no information to go on'
If forced to it he simply won't be able to make a choice if are there are no options available to indicate the choice.