Boeing's disasterous MCAS system relied entirely on a single AOA sensor and did no real sanity checking, yes. The Airbus plane this article is about had three AOA sensors fed through three redundant ADIRU modules, with the data being checked and cross-checked by each of the three primary and two secondary flight control computers, each of which also had an internal monitoring channel running independently-written software on seperate hardware checking its internal calculations.
The reason Qantas Flight 72 only nose-dived twice, if I'm understanding the incident report correctly, is that each nose-dive caused the internal monitoring to fail and that part of the flight control computer responsible to be faulted out for the rest of the flight. After the second nose dive, all three of the primary flight computers had faulted, disabling the affected flight control features.
The reason Qantas Flight 72 only nose-dived twice, if I'm understanding the incident report correctly, is that each nose-dive caused the internal monitoring to fail and that part of the flight control computer responsible to be faulted out for the rest of the flight. After the second nose dive, all three of the primary flight computers had faulted, disabling the affected flight control features.