I generally consider an undefined symbol to be a syntax error.

P:\test> perl -wle"prnit 'hello world';"
Unquoted string "prnit" may clash with future reserved word at -e line
+ 1.
String found where operator expected at -e line 1, near "prnit 'hello 
+world'"
        (Do you need to predeclare prnit?)
syntax error at -e line 1, near "prnit 'hello world'"
Execution of -e aborted due to compilation errors.
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Seems I'm not alone.

The syntax error has nothing to do with prnit being unrecognized. It's a bareword and syntactically considered as if you had said 'prnit' (with quotes). The syntax error is the juxtaposition of two constants. For exactly the same reason, you get an error from perl -wle"0 1". Perl does indeed say "syntax error" only when there is a syntax error, not for an undefined symbol.