Firstly, I've never seen this curl command before and I couldn't find any reference to it in documentation 🤔 Can you maybe try to backup via the JMX console? This is decribed in the Backup and Restore documentation for AEM 6.3 here.
The command using curl looks like this:
curl -u admin:admin -X POST http://localhost:4502/system/console/jmx/com.adobe.granite:type=Repository/op/startBackup/java.lang.String?target=backup.zip
However, remaining on the subject of your particular use-case: A zip bomb is an archive that contains nested archives (usually repeated to a very deep level) which is very small but that when unzipped, will be so large that likely crashes your system. Since the ZIP you are creating contains the quickstart JAR (which itself contains nested JARs and ZIPs), it's not entirely surprising this might trigger a warning in the unzib lib for your RHEL7 system.
If I were you I would try:
Backup via JMX instead, see if that changes anything
If not, ticket to RedHat
Else, you can try backing up to a folder as opposed to a zip maybe?
Eg: "aem_backup.zip" backs up up to a ZIP file, "aem_backup/" backs up to a directory.