I would think "from" means nationals of these countries rather than passengers on flights which originate there.
This is well overdue, a middle aged Canadian couple are a far lower risk factor than an unemployed Nigerian single mother when it comes to overstaying.
Passengers would still have the same scrutiny but as most people in the low risk countries line could be waved through without detailed questioning or extensive checks, things would move a lot quicker. Average time spent in the arrival hall would fall. Immigration officers with the skills and experience to deal with the difficult cases could concentrate on the high risk countries line.
A Japanese business man wouldn't be stuck for an hour simply because his flight landed ten minutes after one from Pakistan.