I think it's more mundane than that, I assume they mean that certain international flights will be turned around or redirected while others will complete their route. Say a flight just an hour underway London to New York might be turned around while one nearly at its destination may be allowed to land.

Depending on the nature of the disruption it may be they simply have drastically reduced capacity to handle traffic so landings may be much slower and they'll manage the traffic based on various priorities.