I’m trying to replace a single pole switch in my room that is used to control a single ceiling light. The replacement switch is a smart switch.
 

However, after taking a look, it seems the wiring isn’t as straight forward as I hoped.

There’s 3 separate cables coming into the box. Each cable has a black wire, a white wire, and a copper ground wire. The ground wires are all fastened to the back of the box, the black wires are all bundled together on the side with a cap covering the ends of all 3, and 2 of the white wires are bundled together with a cap as well as a separate white wire that joins the two to the switch. This leaves one more white wire that is going directly from one of the cables to the switch.

In summary, none of the black cables are connected to the switch but all of the white cables ARE connected to the switch. I checked with a voltage detector and all of the black wires are hot. The 2 white wires that are bundled together and then connected to the switch are never hot, neither in the on or off position. However, the white wire that isn’t bundled and connected to the switch is hot when the switch is OFF not on.

Can anyone explain to me what’s going on here? Here are some pictures:https://imgur.com/a/HLHFBtj