I did think tyre inflator as well, but the shape of the tube spigot, with a rounded edge make me think low pressure - hand or foot tyre pumps can reach very high pressure when pumping - enough to blow the tube off the spigot. Tyre inflator tube is usually has a braided cover, which does not allow a lot of movement to pass over the spigot, and the spigot s usually have a series of conical grooves and need a jubilee clip to hold the tube in place....
It also looks very much like some tap adaptors used with water hoses, but it seems too smaller to fit most tap spouts, and the hose tail looks too small for garden hose as well...