The spurious error message appeared in 5.20 and got fixed in 5.38.

I think the following excerpt from the 5.38.0 perldelta is relevant here:

  Syntax errors no longer produce "phantom error messages"
    Generally perl will continue parsing the source code even after
    encountering a compile error. In many cases this is helpful, for
    instance with misspelled variable names it is helpful to show as m
+any
    examples of the error as possible. But in the case of syntax error
+s
    continuing often produces bizarre error messages and may even caus
+e
    segmentation faults during the compile process. In this release th
+e
    compiler will halt at the first syntax error encountered. This mea
+ns
    that any code expecting to see the specific error messages we used
+ to
    produce will be broken. The error that is emitted will be one of t
+he
    diagnostics that used to be produced, but in some cases some messa
+ges
    that used to be produced will no longer be displayed.

    See "Changes to Existing Diagnostics" for more details.
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Cheers,
Rob