Oh, wait… I just remembered… users have reported that Filezilla does by itself install malware/bundleware, unless you’re very careful to untick some boxes during the installation… IT IS malicious that they install other stuff on your machine and it’s hard for you to find what exactly they installed…
See the Negative reviews on Alternativeto
There’s got to be an explanation, it’s either a false positive, or indeed malware… Try to upload the file to VirusTotal and see what you get