It's called "implied polyphony" or "single-voice polyphony". The solo string works of Bach are excellent examples, and they function similarly to the instance being asked about here. They typically involve leaps in register that break up the sense of one voice. Bobby McFerrin is famous for doing this vocally, creating multiple voice parts by jumping from one register to another. (This is done solo, live, as opposed to his overdubbed recordings.)
A Bach example, his first suite for solo cello, performed by Pablo Casals, who "discovered" them (they'd been forgotten until he came across them):
And here is some implied polyphony by Bobby McFerrin: The Beatles's "Blackbird". This isn't counterpoint, per se, but it certainly illustrates how multiple voices can be implied.