Unfortunately, in case if there are no logs or other RU files stored on the machine, then there's no way for us to tell if it was accessed or not since the log files are only stored locally and we have no access to them - only the user themselves can access the log or setting files on their machine and we only request files to diagnose connectivity or configuration issues. However, as we've mentioned before, if you believe that someone had obtained unauthorized access to your machine (which is illegal), then please consider contacting nearest police department in order to report this - in this case they can request the logs from our servers which might help taking the originating IP address of whoever accessed your machine. You can also provide our contact email email@example.com to the police department.
Unfortunately Linux is not as totally immune to hacks as you may think. Try to read different cybersecurity forums and you'll see. And just like RU support said, it can be accessed in different ways and then make additional installations by the attacker. Lastly, that version that you saw was very likely modified.