Social trust is high because there are pretty heavy handed control measures over the population with havy costs. Thats more of a fear based society than trust. Government can giveth and government can taketh.
1. Fear of a capricious state can cause survival-motivated compliance which can appear as "trust" in coarse measurements. Meaning, you simply do fewer of those things that would provide opportunities for distrust in contexts where that could happen.
2. In a relatively severe, but consistent regime, the high penalties for violating trust in everyday cases (crime) act as a deterrent.
3. Fear may cause people to be selective and mindful about their social associations based on stronger proofs of trustworthiness. You might tell a Hitler joke to someone you have used more energy/caution to "vet", but avoid being too casual in environments of undetermined trustworthiness.