In general, the exit status of any process is defined by POSIX to be an 8-bit (unsigned) integer value, so the possible values are between 0 and 255 inclusive.

> `WEXITSTATUS(stat_val)` [This] macro evaluates to the low-order 8 bits of the status argument that the child process passed to `_exit()` or `exit()`, or the value the child process returned from `main()`. [_wait(3p)_](http://man7.org/linux/man-pages/man3/wait.3p.html)
>
> The C standard specifies two constants, `EXIT_SUCCESS` and `EXIT_FAILURE`, that may be passed to exit() to indicate successful or unsuccessful termination, respectively. [_exit(3)_](http://man7.org/linux/man-pages/man3/exit.3.html)

Conventionally, `EXIT_SUCCESS` is equal to zero and all non-zero values are treated as a sign of an error.

However, POSIX-like shells including Bash reserve a range of high exit statuses for internal use, to signal that something went wrong in the called command without that command having a chance to return an explicit exit status ([Bash manual](https://www.gnu.org/software/bash/manual/html_node/Exit-Status.html)):

> For the shell's purposes, a command which exits with a zero exit status has succeeded. An exit status of zero indicates success. A non-zero exit status indicates failure. When a command terminates on a fatal signal N, bash uses the value of 128+N as the exit status.
> If a command is not found, the child process created to execute it returns a status of 127. If a command is found but is not executable, the return status is 126. 



In practice, any value between 1 and 125 can thus be used to indicate an error in a program-specific manner. As @mosvy hinted in a comment, there was [an effort by BSD](https://stackoverflow.com/a/1535733/5981379) to standardize some meaningful exit codes, but it never became universal. These unified exit codes started from 64, leaving anything below that value for program-specific use. The highest "standardized" value was 78, so it is clear that the values mentioned in your example are purely arbitrary program-specific codes.