It's written using Symphony framework and seems to be using the latest best practice. Nothing to worry about here. PHP has its warts, which are being addressed since PHP 7.x. Modern frameworks like Symphony go even further by encouraging best practices when developing PHP WebApps, unlike the dark old days of PHP WebApps full of SQL injections and XSS issues (still is though in the WordPress plugins ecosystem).
I'm mostly a Python guy and used to look down on PHP, but changed my tune since the release of PHP 7.x. If Python has JIT half as good as PHP these days, I would die happy.