If you did a complete reinstall of the last
Public Release build you would not have
gotten KB4495666.
What did you reinstall?
The moment he switched to the Slow Ring he got the CU
UPDATE 4/9: We have released Build 18362.53 (KB4495666) for Windows Insiders who are currently on Build 18362.30 of the Windows 10 May 2019 Update. This update also includes security updates that come as part of the normal monthly Patch Tuesday release cycle.
The question should be: why did he switch if he didn't wanna be on the WIP anymore?