@GeorgeB If you got paid, then you meet the traditional definition of a professional. You don't need to earn your full-time living doing it.
My definition is different ... You're a professional trumpet player, if playing the trumpet is how you make a living. Of course, it's okay to have different definitions. And I think GeorgeB's definition is very reasonable, too. And I think many would agree with him.
This prompted me to think of some of those who augmented their playing income in order to make a living (so technically not professional players by this standard, but are amply represented in trades media, held significant posts, have multiple commercial recordings etc.):
Rudy Muck (both of them)
To earn one's living just from playing is not just rare today, but always has been rare. At the heyday of major symphonies, the typical performer held at least 2 other jobs to keep food on the table (look up Fred Forman some time - a true performing musician's life).