That's not correct, the added escapeshellarg() call is inside the mailSend() function, which sends mail through php's mail(). See [1].
[1]: https://github.com/PHPMailer/PHPMailer/blame/4835657cd639fbd...
[1]: https://github.com/PHPMailer/PHPMailer/blame/4835657cd639fbd...
From my reading of the code, "only implementations using mail() (ie. not sendmail or SMTP) are affected".