I have no idea why she was so upset.?? Being a parent of four I have ran into alot of parents who don't allow swimming or football, under the predetemined notion that they are "dangerous". Some parents come from very structured and sheltered backgrounds, and pass those traits down to their own children.
My family loves the outdoors and I allow my kids to share that love with others. We bring friends along and my kids can go with other families camping. We do discuss the fact with the parents that we are going camping and where we will be, when we will be back, etc.
Try to share the hammock thing with this parent, set it up the next time she/he comes over, show them how safe and comfortable hammocks can be. Show them the HF site to educate them on the styles and the popularity of hammocks.
The parent may have a preconcieved notion that all hammock people are left-over "flowerchildren" from the '60's, and not just run of the mill everyday folks (who enjoy a comfortable sleep).
As a parent, I do like to know who my kids are with, where they are and what they are doing....all the time..until they are old enough to make good decisions and be able to protect themselves. If the kids are sleeping over at someone elses place, I want to know what the parents are like and what kind of supervision there will be. I dont need my kids going to a "kegger" at age 9, or being exposed to inappropriate materials at that age.
Hopefully, you were freinds with this parent and can rebuild the trust and relationship, for the kids sake.
Possibly, invite the parents over for hammock demonstration, if they are open-minded enough to try something "out-of-the box". It takes all kinds of people to make this world go 'round, not all are adventurers or outdoors people. Some folks camp in Winnebago's and some in hammocks, some do both. My brother-in-law refuses to camp, period. He will stay at a nearby hotel, if we are having a family camp out.?? He hates anything outdoors, weird. My wife is a teacher and is exposed to so many parents, it is hard to believe some folks still have kids. We get to see all kinds, good, bad, ugly, careless, overly protective, spoiled rotten and neglected.
Don't take it personal, until you try to mend the situation, maybe the parent was just having a bad day. "HYOH" AND "RYOK". Hang your own hammock and raise your own kids. Kids come first, love 'em all. Parents ,well thats another story. Some parents have alot of extra baggage, and some don't want their kids going up.
Ambulo tua ambulo.