First, let me diagnose the error. To say that 'cats' is the opposite of 'dogs' is to confuse antonymy with collocation. Likewise for 'apples' and 'oranges.' Both children and adults commonly make this error.
I know of no conventional word for these dubious antonyms (although this page suggests there are terms for different types of antonyms). Pseudoantonym and false antonym sprang to mind. Unfortunately, these words are already in use for a different concept (see here).
You might use folk antonym, where folk means:
Relating to or originating from the beliefs and opinions of ordinary people (ODO)
This is the same way 'folk' is used in the expression folk etymology:
A popular but mistaken account of the origin of a word or phrase (ODO).
Parodying this defintion, we might define folk antonym as:
A popular but mistaken antonym of a word or phrase.