It would make more sense to me if it said "disables" as that would imply that not only were you getting an automatic nose down trim (which both deters further decel through increasing the column force AND places the stab in a good nose-down position to assist recover if high thrust is applied) but also you're prevented from manually overriding that and trimming yourself into a stall.
Since trim is normally enabled, i can't see why you'd add another "enabling" above stick shaker.
Seems to me like a translation problem or a missing word - maybe it means "enabled above stick shaker SPEED" not "AOA"?
Total guesswork based on no specific B737 knowledge, will be interested to see the 'official' answer ...
The MAK report into the Aeroflot-Nord B737 accident states (page 76) that STS is only active below shaker AOA. So either they are wrong, the text quoted is wrong, or the term STS is being used in different senses by the two texts.