That does indeed sound like an automatic adjuster. Under certain situations with enough travel in the shoes, the cable will in theory pull back enough to ratchet the locking tab up another tooth. And if the adjuster is free enough (lube it well with that temp resistant brake grease stuff they sell for sliding caliper pins) it will spin a little and bring the brakes back into adjustment.

SOmetimes I hear that those adjusters only work when the handbrake is applied, othertimes I hear they work when you brake going backwards. I've never really bothered to stare at it long enough to figure out how it works. Some newer cars we have ('89 Bronco II, '96 4Runner) with drums in the back have similar setups and never need adjustment.
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'63 PV544 rat rod, '93 Classic #1141 245 +t