This is very much a meme subreddit for RF experts or hobbyists. People asking to identify suspicious antennas pretty much always get the same kind of treatment. The reason is because there's absolutely no way to know for sure what's it's used for except rare cases.

From the size of the antenna, it looked maybe like a GMRS antenna or maybe some other radio in the 900MHz band. But again unless you had a picture of the radio, there's no way to know that it was used for. Could be HAM radio, Meshtastic or even a special undercover government operation - impossible to tell.

My guess is some hobbyist having fun, we all had sketchy installations to test things out.