Buddy Ryan ran the 4-6 when he was with the Bears.
That had nothing to do with the formation. It was named the 46 after Doug Plank (his number was 46).
From Wiki:
Unlike most defensive formations that take their names from the number of defensive linemen and linebackers on the field (i.e. the 4-3 defense has 4 linemen and 3 linebackers), the name "46" originally came from the jersey number of Doug Plank, who was a starting safety for the Bears when Ryan developed the defense, and typically played in that formation as a surrogate linebacker.