What you are seeing is fairly common. It was easier to run power up to the controlled fixture (light, or whatever), then just run that hot down to the switch. Now, if they did it right, they'd mark the switched wire with a red band of tape to indicate it was switched. So, all the switch is doing is breaking the hot, it's just that it is feeding hot back to the switched thing on (probably) the white wire. red on a single pole switch just normally indicates it is switched, not that it is a 3-way, and is also normal.
On a single pole switch, it doesn't matter which power lead goes where (just as long as you don't hook it to the ground lug!).