Mohamad, 

it is definitely ‘ le Liban ‘, masculine gender. The lesson on this site covers the ‘ rules ‘ of grammatical country gender, with exceptions noted.

I can’t see in the linked text where it is referred to as ‘ la Liban’ - if you have seen it written elsewhere as such, that was an error. 

I can see ‘ La langue officielle du Liban ‘ et ‘ la population libanaise ‘ - the feminine nouns here are ‘ la langue ‘ and ‘ la population ‘.

 Continents/countries/counties/regions/states are masculine, feminine or plural in French (Gender)

 https://www.lawlessfrench.com/vocabulary/countries-and-continents/#L