Yes, this is true. Swifts do everything on the wing including sleeping and mating. The only time they ‘land’ is to visit their nests and unlike similar species they don’t rest on telephone wires.
Swifts can be observed screaming over rooftops in excited flocks during summer evenings and these flocks will often spiral high into the air as dusk approaches. Swifts are very light and can easily stay airborne drifting on faint air currents throughout the short summer nights.
If one is found on the ground and it appears uninjured they can be helped into the air but grounded birds are usually young or sick individuals. For more information visit the RSPB website RSPB swift information