Pretty sure everyone understood, but since you gave the definition, we have to be more precise. You gave the most common definition of the word professional, which is obviously correct, but there are more definitions:
someone who has a lot of experience or skill in a particular job or activity
an expert player, as of golf or tennis, serving as a teacher, consultant, performer, or contestant; pro.
a person competent or skilled in a particular activity
It pretty much depends on the way the word is used and on the context.You don't need to make a living out of what you do to be professional. It is about skill and knowledge and capability as well. Anyhow this whole thing is about being the opposite. Antonyms of the word professional are: unskilled, ignorant, incompetent, inefficient, stupid, inept, rookie, untrained, incapable and indeed amateur. In my view people who want to have only fun are FSR's tumor and are one of the reasons for the decreasing level of competition. They are destined to fail in any competition, as they are unwilling or unable to make sacrifices or employ brain cells for progress, performing as well as general functioning in FSR. Testing pointlessly thousands of laps doesn't make anyone professional if they don't avoid acting upon the above mentioned definitions of hobbyist (amateur). I prefer the term hobbyist as its less emotionally colored and also for the historical reason I've mentioned in the other topic.
Unfortunately the percentage of hobbyists is indeed very high, I would guess around 90%, which partially explains the results in the past 4 years. To investigate this, I would make a poll asking everyone whether they know and read the FSR rules, I think already there you can disqualify at least 70% of all FSR drivers from being professional. These hobbyists bring down the rest with them, hence the protesting issue among other stuff.