A MkV Golf would have had its warranty run out, so the dealer is not going to perform the entire scheduled maintenance/inspection/certification as they would for a car under warranty or going to be resold by them. This would include:
- Visual check of the battery (is it leaking? cracked?)
- Check the "magic eye" - the indicator (green, black, yellow) of battery health
Only if they saw something obviously wrong (corrosion all over, leaks), non-green in the magic eye they would continue with an actual load test. The service technician is going to mark the battery as good as he started up the car, heard it started normally without slowness, didn't see any voltage light on the dash, and the above 2 things checked out.
Your battery was nearing 8 years old if the car was sold in 2008. The lifetime of a battery is generally expected to be 4-5 years. Cold weather, rough conditions, not keeping it charged and low water will all contribute to less battery life.