This technique (redirecting through some dummy ?url=... page) is a common way of doing an external redirect on any service you're building. It's a simple way of making it impossible to see the actual Referer to external website, which is more secure to your data and the service you're building (e.g. Gmail).
Code usually doesn't carry final HTML in its data structures, whereas converting a URL in a single place where it's extracted is easy. In other words, making sure you didn't miss to put rel=noreferrer everywhere is way harder.
Because I've done tracking like that for several years, lots of services are still doing it this way and because rel="noopener" or rel="noreferrer" is the way to go if you want to mask the referrer. Even Google recommends to do it that way[0].
If you are not using it for tracking, there is no point in doing it like this after all.
