You have to know something about Bird's era that the stats will only tell you if you go looking. Everything was run through PGs. Assists were racked up almost exclusively by PGs, who generally were the smallest people on the floor.
Then Bird and Magic came in the league. Guys who should have been PFs, players who set up down low and played close to the basket, were now people who were the most creative, dynamic passers and movers of the ball. Straight from the first moment they entered the league, their offense and ability to create for others was the best in the league and at an all world level.
Big men being the league's best passers was unheard of. And not just bigs who could pass some and rack up some stats while in a team system, but creative and exciting passing that elevated the level of how basketball was played. They brought a form of showmanship to the game.
Bird was a big in those early years and the offense was run through Tiny because he was a star PG and that's what offenses did then, they ran through PGs. So for Bird to be a top 15 in the league in assists per game while essentially playing as a 3/4 big was unheard of. Once Tiny was gone, Bird took over the main facilitator role at SF because Fitch was gone too, so K.C. gave the team facillitating role to Bird.
Bird's passing stats don't tell the whole story of just how good a passing big man he was.