My guess would be one of 3 things:
1. This is a person who knits extremely tightly, and so size 8 worked for her.
2. This is an older British knitter who was thinking of the old UK size 8, which is 4mm (US size 8 is 5mm).
3. It's a typo.
I would go down as far as you need to, to get that gauge. Even if it's a size 1 needle, it doesn't matter-- the gauge does.
And you're welcome!