of course you can run Cron as well and run all your jobs twice in two different ways, but that's only pedantically possible as it's a completely useless way to do things.
systemd itself only has 2 references to "crontab" in its entire codebase and both of those are in man-pages.
My educated guess is that some other package is installing a generator to generate systemd units out of the crontab (e.g. https://github.com/systemd-cron/systemd-cron)
of course you can run Cron as well and run all your jobs twice in two different ways, but that's only pedantically possible as it's a completely useless way to do things.