Generally speaking, Ruslan
is derived from "rus" - the Slavic word for "fair, blond". In the eastern-Slavic folklore most beautiful women are blond (hah!), so maybe that's how the site you are citing decided Ruslan
However, unlike other Slavic names, Ruslan
is popular in the eastern (predominantly Muslim and definitely non-Slavic) parts of the former USSR. That has lead some to believe that the name is influenced by the Persian word "aslan" - a lion.
I personally think that the name does come from "rus" (other Rus- names are common among Slavic people), but the eastern people of the former USSR linked it with the more familiar "aslan".
Having said that, I am surprised you found the blond-explanation on a Kazakh site and the lion-explanation on a Ukrainian site. Those should be reversed! :P