The number regexp uses \d to imply [0-9], where this is not true unless the /a flag is active (which it is not, it'll match anything that has the "Decimal_Number" property)
perl -e 'use JSON::Decode::Regexp qw(from_json); use Data::Dumper; print Dumper from_json("[1\x{16A61}]")'
Argument "1\x{16a61}" isn't numeric in addition (+) at /opt/markperl/lib/site_perl/5.22.0/JSON/Decode/Regexp.pm line 163.
$VAR1 = [
'1'
];