Can someone help me understand why stud finder is showing a stud behind my thermostat?

I'm not sure if this is the right place to post this so I'm sorry if not. I'm trying to replace this Honeywell thermostat with an older Nest Thermostat E. When I tried to install the thermostat, I felt like I was hitting something behind the wall. This was a few months ago. Now, I got a stud finder and it is showing what seems to be a stud below where my thermostat is.

If I flip the stud finder upsidedown, I get about a 6" x 6" my space where it is throwing the stud finder. The stud does appear to be right next to it. Could this be something extended off the stud for support? My biggest fear was that I was going to screw into the wires (which is my biggest fear every time I replace a thermostat lol).

Any help is super appreciated, I just don't understand what is happening. Thank you!

P.S. - Ignore the wall, it is my childhood home and I loved blue tac when I was a kid lol. It is going to be painted soon though.