Mystery snow shovelers

We had a light snow two nights ago. The next day, the snow ended and since I live on the "sunny side of the street" I usually let it soften things up for a few hours before I shovel. Midafternoon, I put on my boots, went outside and... WTH? My sidewalk and stoop were already shoveled and salted! Wow, what nice neighbors I have!
I looked at the security tape to see who to call and thank but that's when it got weird. I saw a white van, two hispanics guys (I could hear them talking on the video) hopped out, grabbed shovels and went to work. They finished in about five minutes, got back in their truck and drove away. They didn't even ring my doorbell. I don't have a clue who they were.