It looks like you got something between the pad and the rotor, perhaps a small stone or piece of gravel.
Sometimes this sort of thing happens with semi metalic pads even without a foreign object getting in the way. That is how my rear rotors looked when I replaced them about a year ago. The grooves also came on somewhat suddenly, but they were there for a few years before I changed the pads and rotors.
It is normal for the pads to contact the rotors, and for that matter to create a little bit of resistance to turning. Does the problem wheel have more resistance than the other side after cleaning the junk out of the way?
If so, gently sand the pads, if there is any imbedded foreign object (gravel, glass, etc) remove it, reinstall the pads and drive home.
Once you are home, you can decide if you need to remove the rotor and have it machined or replaced or? The grooves arn't good, but they are not dangerous either.
