You're right that a "true" loop would cover 360 degrees more or less, so you leave in roughly the same direction you came in after going around the circle and crossing over (or under). There are a lot of others, though, that don't cross over; they cover more than 180 but less than 360 degrees, and you leave in roughly the opposite direction from where you entered. Cantara Loop and some of the others mentioned above are like that.

They weren't called "loops" at the time but many of the curves on the Mount Tamalpais & Muir Woods railroad would definitely have qualified under the relaxed definition. Check out the Double Bow Knot.