In their famous book "How Democracies Die," Levitsky & Ziblatt talk about guardrails. These are the informal rules, not in the constitution, that help hold democracy together.

https://medium.com/p/90d7b191703d

I would say this "tradition" is one of those informal rules. It happens in nearly all electoral races in Canada. But when the results are close, it should be withheld until the courts determine the final tally.

BTW, there is always some administrative errors and cheating in most elections.