According to their numbers, less than half the "symptomatic cases" resulted in a medical visit. Based on information from their FAQ[1], it seems that column represents the total number of people the CDC estimates got the flu that year:
> How many people get sick with flu every year?
> CDC conducts surveillance for people who see their health care provider for flu-like illness through the Outpatient Influenza-like Illness Surveillance Network (ILINet); a network of thousands of health care providers who report the proportion of patients seeking care for flu-like illness weekly to CDC. This system allows CDC to track levels of medically attended flu-like illness over the course of the flu season. CDC does not know exactly how many people get sick with seasonal flu each year. There are several reasons for this including that ILINet does not include every health care provider and monitors flu-like illness, not laboratory-confirmed influenza cases. Also, flu illness is not a reportable disease and not everyone who gets sick with flu seeks medical care or gets tested.
> CDC uses mathematical modeling in combination with data from traditional flu surveillance systems to estimate the numbers of flu illnesses in the United States. CDC estimates that flu has resulted in between 9.3 million and 49 million illnesses each year in the United States since 2010. For more information on these estimates see CDC’s Disease Burden of Influenza page. For more information on CDC surveillance systems, see CDC’s Overview of Influenza Surviellance in the United States.
The way I read that, from the CDC's POV if you aren't symptomatic you didn't get the flu. Similarly, if you are symptomatic it doesn't necessarily mean you did get the flu.
[1] https://www.cdc.gov/flu/about/burden/faq.htm