A number of other, similarly described, instances of people experiencing a presence, particularly of being watched from behind have been attributed to low-frequency vibrations.
Apparently, oscillations (especially in the inaudible 17-19Hz range) can cause vibrations in the eyeball which create a sense of "presence" in the peripheral vision. Frequent causes of this phenomenon are household appliances like washing machines, tumble driers, ceiling fans, etc., but natural occurrences of infrasound have also been found in some "haunted" sights, like the Edinburgh Vaults.