Question

Aren't ' anthe' articles? because in the 2nd video on parts of speech it is said as adjectives

Answer 1

yes they are articles.

Answer 2

a,  an,,  the  ---  are    called    articles.    They are always prefixed before a noun.
These three words are also called determiners.

Since they are telling about a noun, and are written just before a noun,  they are perhaps called  adjectives.  But normally we do not say that they are adjectives.