I agree with the "tech took it out for a spin and hit something" approach. Swapping tires/changing pressures/etc can cause it to pull to once side or another slightly, but driving straight down a flat road and your wheel is now crooked and didn't use to be? That screams something in your alignment/steering rack has been changed from when you dropped it off.
This is just a fine example of why no one ever works on my car but me. In-warranty work just means you've got a stupid monkey screwing things up on your car that you're not paying. Only slightly less annoying than actually PAYING some stupid monkey to mess up your car.