We don't know for sure what kind of breach compromised the data on Bezos's phone. However, public reports have tied the Saudis to groups such as NSO (Pegasus zero-day malware for iOS) and Hacking Team (numerous Android exploits). So, from what has come out, pattern would suggest that it was some kind of zero-day malware activated via link embedded in an email - this would not be a Stingray use case.