Is free evening parking in Belfast City Council car parks the same at Smithfield and Bankmore Street?

No blanket rule should be applied to those two car parks.

Visit Belfast specifically notes Smithfield and Bankmore Street as exceptions when describing many Belfast City Council charged car parks being free outside normal charging hours. Check the current entrance notices for the individual car park, especially if you need to collect the vehicle late. This is separate from on-street controlled parking, where a non-charging period does not override other signed restrictions.