Note that they said that you won't be able to enter as 'temporary' residents. When you showed your expired PR card (or your landing paper) to immigration, they will NOT admit you as temporary residents, but they will be able to establish that you are PR, hence, admitting you as a 'permanent' (not 'temporary') resident 
Technically, what they said, too, was not wrong
Technically, what they said, too, was not wrong