It's unclear from the "post" (what is it with these blogs where entries are like 3 sentences??): did they take current top 10 stocks and project their retuens backwards, or did they look at the retuen of always holding the top 10 stocks in the index?

If the former then duh! Top 10 stocks are top 10 because they were going up! You will see this for any index.

The latter would make sense but given the laconicity of the post, it's pointless to speculate.