Sure, since the difficulty can only raise in three bands 2%, 6% and 10%, and decrease to whatever level is necessary (upto 4x) where is he getting this 20% figure from?

If we are at target hash rate it will maintain that level within 2%. The other thing to consider is the target hash rate is more like "the maximum" wanted, it's different to BTC where 10 minutes is "Desired". "3 minutes" isn't necessarily desired in SolidCoin, it's the maximum.