a successful print returns true (see print). So your prints are equivalent to

1  ?  "3: Flag is up\n"  :  "3: Flag is not up\n";
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and that's a constant expression that evaluates to

"3: Flag is up\n";
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That's a constant that isn't used for anything -- a constant in void context.

When you get errors or warnings you don't understand try adding use diagnostics;. It will try to explain the error or warning given.