Just downloaded using the link on the front page (on Linux) and ran it through ClamAV. It finds nothing.
Running some of the *.exe's though VirusTotal seems to result xonotic-x86.exe being picked up by Rising. Mainly seems to be because it's a portable executable. Even the non-cloud version of Avira doesn't pick it up, so I suspect it's using Rising in the cloud back-end and that's how it's getting the false positive. I didn't run the .zip through VirusTotal as it's got a file size limit of 128M.
Detail:
AV used: Rising
Detected as: PE:Malware.RDM.02!5.8 [F]
AV Update used: 20160416
As Splat said, this appears to be a false positive.
Note: Exact same file (same SHA256 hash) run through VirusTotal 7 months ago, nothing picked up.
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