Generally this means the person's anti-virus has deleted the first copy and they are downloading it again - this could happen a few times until they figure out how to tell their anti-virus not to do that. (Not because your game has a virus in it - just because some of the free anti-virus software does that by default to anything they don't know.)
Or if they don't have stable internet, it might result in multiple download attempts.
Sometimes people don't find where they download stuff and then just download it again...