You were most likely told wrong. Here's the Oregon statute:
ORS 811.490 Improper opening or leaving open of vehicle door; penalty. (1) A person commits the offense of improper opening or leaving open a vehicle door if the person does any of the following:
(a) Opens any door of a vehicle unless and until it is reasonably safe to do so and it can be done without interference with the movement of traffic, or with pedestrians and bicycles on sidewalks or shoulders.
(b) Leaves a door open on the side of a vehicle available to traffic, or to pedestrians or bicycles on sidewalks or shoulders for a period of time longer than necessary to load or unload passengers.
(2) The offense described in this section, improper opening or leaving open a vehicle door, is a Class D traffic violation. [1983 c.338 §655; 1985 c.16 §320]
22517. No person shall open the door of a vehicle on the side available to moving traffic unless it is reasonably safe to do so and can be done without interfering with the movement of such traffic, nor shall any person leave a door open upon the side of a vehicle available to moving traffic for a period of time longer than necessary to load or unload passengers.