It turns out the kid was 8 lbs 6 oz, not 8 lbs.
6lb is within normal at that age. Small would be ~5.6lb.
Having a 10lb+ baby is not normal nor something to be particularly proud of.
I think you are using the 2500 g cutoff, which is true at the start of what is considered a term baby - 37 weeks. However, small for gestational age is usually defined as a weight below the 10th percentile for gestational age. At 40 weeks, the 10th percentile would be around 2800 g, which is more than 6 lbs. In fact, according to graph below, it's more like 2900 g or so at 40 weeks.
And here's the growth curve in British Columbia:
BTW, the new prince was born at ~41 weeks.