The exponentiation arithmetic operator in PHP is **, and only exists since PHP 5.6
The ^ operator is only the bitwise XOR operator.

See:
http://php.net/manual/en/language.operators.arithmetic.php
http://php.net/manual/en/language.operators.bitwise.php

The wrong code is here: https://github.com/squizlabs/PHP_CodeSniffer/blob/master/CodeSniffer/Tokenizers/PHP.php#L1307

 case '^': $newToken['type'] = 'T_POWER'; break; 

I'm not familiar enough with PHP_CodeSniffer's code yet, so I cannot make a PR now, but I'm sure that this is a tokenizer bug.