Which situation is an example of? "relational context" in the transactional model of? communication?

An example I believe of relational context is when I was out with my son on the weekend (he has a developmental disability) and we had agree I would buy him a 1/2 sub sandwich the day before but then he said I would like a McFlurry so I said okay and then he said so you mean I can have a McFlurry and a sub and I thought oh oh I stuck my foot in it so I said but it must be only a 1/2 sub so he said no I want a full sub then and no mcflurry so I agreed so from the original 1/2 sub idea the idea evolved to a full sub which was affected by the warm sunny summery weather in the afternoon and seeing people lined up at ice cream shops so the idea developed in relation to the weather, how hungry he was and the social aspect people buying ice cream.