We followed public health advice. Airport screening and travel restrictions tend to be bullshit in that regard.
Then why are we restricting travel now?
If Sophie Trudeau didn't go to the UK she wouldn't have contracted COVID-19 there and brought it back to Canada. If Joe Blow didn't travel from his house to that public gathering and contracted COVID-19 there he wouldn't have brought it back to his house and infected his family. The point is to slow the spread and flatten the curve. If every country immediately banned all travel the moment the outbreak occurred in Wuhan it would have made a big difference. This situation is unprecedented in modern history, I guess we'll now know better for next time.
Airport screening may not be very effective. Immediately mandating by law a 14-day self-isolation for all travelers would have been better. Hindsight is 20/20. I think next time countries will act more swiftly. Maybe next time we'd do what we're doing now a month or 2 earlier.