The photo in question was taken over a year ago now, I had no intention of selling it at that time. So are you saying that all photos that are taken and someday maybe sold randomly is a commercial act? How am I supposed to determine when I am out taking photos that I am operating at a commercial level or tourist level?
We have the same thing here with our city parks... and all I can say is "it's in the rules". Once I do sell a pic taken there, if I do, they've got the right to their fees. TECHNICALLY, they can fine me much more than the cost of the permit, but they typically take the same stance of offering a "retro" permit for the day. Of course, I haven't had to go through all of that as of yet, but I've known a few folks that have.
I *HAVE* shot family portrait sessions, etc. in the parks, and unlike many photog's in the area, I paid for my permit up front. While I was in there, I got to chat with all the nice folks and found out that the money all stays in the park. Beautification, landscaping, tree care, the works. The "government" funding for the park doesn't cover quite enough to cover the actual AMAZINGNESS of the area, so the little permit fees, covered table reservation fees and donations cover the rest. Granted, I'd rather not pay it, but knowing it keeps my area photo-worthy, I don't mind.
Ours, even just for the city park, is $25/day, or $250 for the year. Thinking of going yearly for 2015, as 10 shoots covers that, and I've got the rest of the year for free. (I'll still add the surcharge for clients, of course.
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All of that to say this... 1) They are being friendly, as I'm sure there's something that allows for a healthier fine. 2) Now you know, so you can earmark all future photos as "Not for Sale" or "Donated for use with permission of...xxxxxx Park". 3) Surely, somehow, some way, you're helping to maintain that small bit of nature?
Now, back to work I go, wishing I had a photo that was widespread and popular enough to even draw that kind of notice!