Don't understand this electrical problem

I have a Xiaomi wireless door/window sensor from which I’ve disconnected the reed switch and soldered on wires. I’ve done this with a few of these sensors (about four others) and they all work fine. However, with this sensor, if I touch ONE of the ends of the wire (not the other) the circuit is deemed to be completed. If I touch the other end of the soldered on wire, nothing.

I’ve removed the wires and now if I touch one or other of the solder pads where the wires were soldered onto, I get no reaction, as you would expect. If I connect both pads with tweezers or wire, I get the reaction you’d expect - circuit completed!

Anyone know what was going on with the wires?! I’ve never had this happen before. Could a bad solder joint cause this? If so, how?

This is just academic - I have desoldered the wires and the problem has gone away.

thinking out loud, is your wire straight?
if it’s coiled, you touching it will probably bring some static electricity to it, and electricity in a coiled wire = magnet…