People who believe this are confusing cat behavior with dog behavior. Although there are some unfortunate cats whom are actually allergic to flea saliva. These poor cats will literally tear themselves up with excessive grooming and scratching. It is quite possible for indoor cats to become flea infested. Usually this happens in households that contain untreated dogs, or as in your case,a brief excursion into the great outdoors.
Fleas are hardy parasites that thrive in warm, humid climates.
An untreated cat can support a colony of 60-100 fleas. The average life span of an adult flea is only six weeks but during that time a single female flea can lay an average of 20 eggs per day. In six weeks a colony of 60 fleas could lay 54,000 eggs. Depending upon where you live, in the winter flea eggs, larvae and adults generally die off. Just remember that any fleas, eggs, and larvae already in your home will continue to thrive.