But researchers from Security Research Labs prove this claim wrong. Regarding this team have developed a small app that will tell you about the security patch levels and also inform you about the vulnerabilities.
SnoopSnitch, download this app and it is for free.
Once the app is downloaded, run it and then click on Android patch level analysis which appears at the top of the screen, and then on Start test.
For completing the test it will take some time like 5-6 minutes, so be patient. This test will go through your device checking whether the patches that the operating system claim are installed have actually been installed.
So go ahead and try this and check whether your device is prone to some vulnerabilities.
Comments your results screenshot and also with the device name.