It says in the class description of CIM_ComputerSystem.HealthState:
Product Specific Usage:
i. HealthState = 5 ("OK") when system is in H0 health state
ii. HealthState = 20 ("Major failure") when system is in H1 health state
iii. HealthState = 25 ("Critical failure") when system is in H2 health state
iv. HealthState = 30 ("Non-recoverable error") when system is in H3 health state
The Host instance (ManagedSystem) always returns 5.
The AMT instance returns 5, unless:
1. AMT is disabled by SKU (returns 0 – Unknown).
2. Watchdog of computer system health expired (returns 20).