The timeline is set out within it.
From my reading, going from memory.
Border Force Officer is sent out to check on things.
Has a chat to port authority.
Gets the vibe that everything is OK re COVID.
Department of health already put the ship in the low risk category so weren't going to make an appearance.
Border force says it's OK to disembark in the sense of passport checks and customs but asks for confirmation re COVID.
After disembarkation he gets emailed the form which he misinterprets.
Perhaps confirmation bias.
30 hours later the penny drops.
Presumably they have learnt from this for the future when asking questions about COVID.
