[Umofomia]

> That's hard to guess. There are three common measure words meaning "pair" [...]

> If you actually wanted one chopstick, you'd say 一只筷子.

Traditional Chinese script versions of Simplified 只 and 双 actually make this more apparent, where they would be 隻 and 雙, which are pictograms illustrating one and two birds in a hand, respectively.