If only GData and avast detect it - GData uses avast as one of its two scanners so counts as 1 detection and almost certainly an FP.
Send the sample to avast as a False Positive:
Open the chest and right click on the file and select 'Submit to virus lab...' complete the form and submit, the file will be uploaded during the next update. A link to this topic wouldn't hurt.
Or
You can send the sample to avast as a False Positive. From the avastUI > Support > scroll down to the 'Report files to the avast! virus lab' Submit to virus lab... button, use the next window to navigate to the suspect file.
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A .part file is an incomplete download, so I don't know if this could also have an impact on what is meant to be a Heuristic detection.