Overloaded operator handlers sometimes receive operands in reversed order, but Perl will notify the handler when it does so by setting the swapped argument to true.

overload:

Three arguments are passed to all subroutines specified in the use overload directive (with one exception - see nomethod). [...] The third argument is set to TRUE if (and only if) the two operands have been swapped. Perl may do this to ensure that the first argument ($self ) is an object implementing the overloaded operation, in line with general object calling conventions. [...]

You probably disregarded that argument?