How is this possible if I have accounted for all possible types?

'some string' is a literal. It is not a reference to anything. I presume you though that ref() would report scalar.

$foo = 'bar';
print '$foo is a ', ref($foo), $/;
print '\$foo is a ', ref(\$foo), $/;
__DATA__
$foo is a 
\$foo is a SCALAR
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