If you specify wildcards on the command line without any quoting, then these are expanded by the shell before restic sees the parameters. This is also the reason why the list of file to backup includes /opt/www/nextcloud/data/updater.log.
restic backup --exclude /opt/www/nextcloud/data/*.log is expanded by the shell to something like
restic backup --exclude /opt/www/nextcloud/data/example.log /opt/www/nextcloud/data/updater.log
This command line requests that restic excludes /opt/www/nextcloud/data/example.log and backups /opt/www/nextcloud/data/updater.log. The correct syntax would be something like this:
restic backup --exclude "/opt/www/nextcloud/data/*.log"
Note the quotes around the file name.