More then likely their land was land owned by the Army Core of Engineers like a lot of flying fields... The Army Core lets them use the land and the club is supposed to verify that the people flying are covered by the AMA. The AMA provides members with insurance to cover any accidents that happen to property in the event of a crash. This was probably their main concern...
I am a AMA member and have my so called "license". The license posting on their board is normally to identify what frequency your radio is using. Having more then one person on the same frequency can be a very bad thing. The board is done as a precaution at most flying fields. We are starting to see less and less of this as the new radios use 2.4GHZ spread spectrum technology. The radios and receivers change frequencies every 2000ms and it is virtually impossible to be on the same frequency now even with 25+ people flying at the same time.
Now as far as having to be a paying member of the flying field; I have no clue. If they called the police, I don't think they would have done anything about it...
I have been looking for a club to join, but in the mean time I went to several flying fields around and was welcomed with open arms to every one of them. I was allowed to fly my own aircraft several times on their fields without being a member of that club. Towards the end of last season I finally settled down with this one club that I like, but they haven't re-opened their membership yet. However to this day they still allow me to fly there as much as I like, free of charge. In return I have been to the field for mowing/weed eating/clean up days to help out with the field...
Go pick up a cheap little plane and try it out if you have been wanting to get into the hobby... Personally I would suggest getting a
GWS Pico Stick Slow Flyer as this is an EXCELLENT first flyer. Just add a radio and battery pack and you are in the air within a couple hours work. Much better than getting the cheap Air Hogs stuff that will fall apart or the LiPo battery will stop charging after 5 charges...
The hobby is great, so don't let one elitist ruin getting into the hobby. Unfortunately you will run into people like this in anything you do... Hell... Even here on BYOAC it is pretty easy to see the people who consider themselves the elitist are.