IMHO, a 3 year old who is reading is an "early reader" by any definition, much the way a 9 month old is an early walker despite the fact that someone else's kid walked at 6 months.

(For comparison, my DD, whom I'd consider to be neither early nor late, started reading at 5y5m.)

My kid plays her cards close to the vest. Every once in a while I see or hear something odd, but mostly not.