The gap exists because the benchmark blends every property type, apartments, row and townhouse units, semi-detached and detached homes, into one composite figure. Detached family homes sit at the larger, costlier end of that blend, so the citywide number understates them on its own.
Neighbourhood widens the range further. A newer east side family home in Willowgrove or Rosewood, an older two storey in Erindale and a character home in Nutana are three different markets that happen to share one city, and none of them prices off the citywide average alone.
The number that actually matters is what a specific family home is worth against real comparable sales, not a citywide composite. Get your hand-reviewed valuation from Joel Dyck.