Not alone on the trail

My buddies and I were looking for a trail in a local canyon. We noticed the north facing side was covered in snow while the south facing side was dry. The problem was the south side was private roads filled with vacation homes. These were not regular cabins, they had crazy architecture and villainous style. They were all empty except one friendly old man who waved from his third story deck. Figuring nobody was really around, we decided to hike there briefly. The trail apps didn't show any trails but we found one avoiding people's yards. After a few minutes we had a nice view of the neighborhood below, with just mountain for hundreds of miles.

We started finding things hidden in bushes and trees along the trail, all in ziplock bags without weathering, as if just placed. At first it was innocent items like tennis balls or sealed CBD tinctures. We figured it was a scavenger hunt for the rich residents since it was their private trail. After finding more, we even discovered nice earrings taped up in a box, also ziplocked. When the trail faded we headed back after a few hours.

Nearing the bottom but still above the homes, we found a ziplock in a stick teepee off the trail. Inside was a silky black bag containing women's panties and a nice vintage chain in its original box with a jeweler's business card. We started to put it back, thinking it was some weird game. But I realized the chain could be valuable, so I grabbed it and said "I'll take this." Right then we heard three ridiculously loud bangs from above that sounded like boulders. Clearly above us but not far, though nothing was visible. I quickly put the chain back, rushed to zip the bag, and we sprinted to the car. A homemade trespassing note with a photo of our license plate was on the windshield.

My theories: 1) The rich people have cameras and speakers to scare trespassers since cops likely ignore it. 2) They plant stuff to charge us with stealing. But that doesn't explain the sound. 3) A stretch, but someone planted evidence to frame us.

I'm curious if anyone has experienced this. We may have just heard a boulder fall during their scavenger hunt.

What do you think?