Oil "mists out" all the time, possibly enough for drips on the floor at the change of seasons, heating coming on and off, etc. That is the reason you don't get as much oil out at the annual or 5000km change as you put in. Under almost any circumstances short of immersing the Rohloff in water, for instance by riding through a stream over the hub, there will be enough oil in it to cover all the gears in a thin film, which will be enough to protect it at least in the short term.
Some external oil is natural. If the Rohloff were built to be oil- and air- and water-tight, it would be too heavy for bicycle use.
However, in your case, where you were not present to see how much oil emerged, I would argue differently. The Rohloff is an expensive component, so it is as well to change the oil after any threatening event, like an immersion, or perhaps after an oil loss of unknown magnitude, as this one appears to be. The opportunity cost could be £1000+ for a new Rohloff; the cost of reducing the uncertainty and achieving peace of mind is under £20. Since the hub "works normally", it is not panic stations: an oil change as soon as is convenient will probably be good enough.
