To be pedantic: there is no such thing as a boolean value. It’s all just bytes and larger numbers behind an abstraction that allows a higher-level programming language to implement Boolean algebra by interpreting numbers a certain way. One such abstraction is the POSIX convention of treating a return code of zero as success and everything else as a failure. This consequently defines how Boolean algebra is implemented in POSIX-compliant shells:

• The if statement tests the return code of the command specified in the header, then executes the then branch if the return code is zero, the else branch otherwise.
• The while loop similarly tests the command in the head and executes the body if its return code is zero.
• The boolean && and || operators treat zero return values as true and nonzero return values as false. Go try it out.
• Even the true and false commands are just programs that immediately return 0 and 1 respectively.

If you start treating nonzero return codes like a success value with meaning, the only thing you’ll achieve is that your scripts won’t be compatible with the shell. stdout exists. Use it.