Yes, your guess is right. Nextcloud apps will interact with cron.php as described in Nextcloud manual:
cron.php is an Nextcloud internal process that runs such background jobs on demand.
Nextcloud plug-in applications register actions with cron.php automatically to take care of typical housekeeping operations, such as garbage collecting of temporary files or checking for newly updated files using filescan() for externally mounted file systems.
You can schedule the cron job as better suits you, in the example it is set to run every 15 minutes.