After more investigation, I thought that those strange score may come from some one who incidentally clicked roborumble.bat without proper configuration which however I never reproduced.
Using the latest robocode version as accepted one and allowing Anonymous uploads is risky as robocode has a lot of downloads per week and anyone who incidentally clicked roborumble.bat contributes without verifying configuration.
Maybe we should also modify roborumble client to add a field usually called "User Agent" and upload OS/Java Version etc. so that strange scores should be more trackable.
Another option is to disable Anonymous uploads when using the latest version of robocode, but this would only prevent incident roborumble runs and wouldn't verify user agent.