Hey,
that's because it's right how they use it ;)
Grammar is a bitch 😋
Hope this can help you to understand:
Singular (just 1)
First person:
I am
Second person:
You are
Third person:
He/she/it is
Plural (more than one)
First person:
We are
Second person:
You are
Third person:
They are
thanx. but still not clerified me yet