Sounds like the rear sensor that mounts in the spindle could have been damaged or the speed ring thingie damaged when the wheel bearing was replaced. The mechanic will be interfacing with some abs components when changing a wheel bearing, as the bearing is intergrated into the rear drum. The mechanic should fix this.
Parking Lot Hero
2008 WRX daily driver
2003 ZX3 23D Autox Car 42 FSP
"Hella Functional - Raced, Not Hard Parked"