Sounds like they did a lot to the car - but none of what they have done should have caused a problem with the VSC system.
I can see the timing belt with water pump and thermostat - good thing to have done every 60K-100K for the timing belt (water pump is right behind it - saves you quite a bit of labor to have it done at the same time). Plugs are normal routine change (every 60K for platinum tipped plugs). Injector service - the car probably didn't need it - sometimes they make the car run a bit odd afterwards.
Some systems are a bit more sensitive than others - I remember a case where a cell phone plugged into with a 12V charger caused the yaw sensor to report a problem, kicking on the VSC lamp. The light should have reset with a scan tool - if it comes back on immediately afterwards - then I would suspect the shop probably screwed something up.
Good Luck.
2002 Corolla S, Silverstream, 1.8L 1ZZ-FE (VVT-i)
2003 Matrix XRS, Cosmic Blue, 1.8L 2ZZ-GE (VVTL-i) - RIP
2009 Matrix XRS, Blue Streak, 2.4L 2AZ-FE (VVT-i)
