Furthermore:
Is there anything different in index1.html and index2.html from index.html, like color schemes?
It could also be the name, as most people only use index.html and a second index may seem suspicious (as in someone hijacked the website and added an extra index that looks the same. Sometimes links go to the index.html instead of /, so if hackers have hijacked the website, then they can lure you using a similar url, i.e: index2.html, which might be what Google thinks is going on).