VirusTotal doesn't actually do a site scan as such, just checks blacklists, etc. Hence why you don't see Avast or AVG in the supposed lost of scans.
The three links that I first posted actually do site checks looking at vulnerabilities/weaknesses that could be exploited. As I said this could result in Avast alerting, but avast doesn't do these kind of checks, it is simply looking for malware/phishing, etc.
What I say holds no sway as to why avast may be alerting on your site, which is why I also gave you a link to report it as a possible false positive.