conjunctions of two

Mom took Su to the roof this afternoon, playing his remote control toy car.
they bumped into neighbors with their big dog.
Su said,
"大," "驚驚;"
"小," "無."

1. is Su good enough to speak to make conjunction of two major meanings?  what's more important, make a comparison between big and small, and his feelings towards them.
2. since the Small does not exist when the Big is seen, he has an abstract thinking.
3. or, he was just saying "the Small is NOT here" instead of "Not Scared?"
(this inference was already rejected by Su's mom.  She repeated Su's saying, adding extra meaning words, and asked for his confirmation.)
4. what is his motivation to express this comparison since no one asks?
5. why this expression is such important to speak out when he is experiencing an emotion of threat and scary?