In C/C++, it's very common for a function to return an integer corresponding to any errors that occured within the function, including a "success" error code, because it has to return something, otherwise it's undefined.

I'm not sure that's what happened here but that's why "successful" errors are a thing. Somewhere it got misinterpreted maybe.

https://www.man7.org/linux/man-pages/man1/bash.1.html

Lists A list is a sequence of one or more pipelines separated by one of the operators ;, &, &&, or ||, and optionally terminated by one of ;, &, or .

   Of these list operators, && and || have equal precedence, followed by ; and &, which have equal precedence.

   A sequence of one or more newlines may appear in a list instead of a semicolon to delimit commands.

   ....

   AND and OR lists are sequences of one or more pipelines separated by the && and || control operators, respectively.  AND and OR lists are executed with left associativity.  An AND list has the form

          command1 && command2

   **command2 is executed if, and only if, command1 returns an exit status of zero (success).**

So, command 1 returns success, but command 2 fails. The FAILED comment at the beginning of the error message is the message to parse, one part succeeded, the other failed.

Not using && and running your command by line will show where the error is.