no it is not a typo, 

mouth is translated to  فم  and that's correct. However, if you are talking about someone who is not present at the speech  you say فاه

if you are talking to someone about his mouth you say فاك  eventhough فمك  would be completely true

but both of them are correct

also the plural is أفواه  and it is irrigular prular. 

so the word is correct and it means mouth and completely equals to the other word فم

This is a special kind of irregular words in arabic 

اسمها قاعدة الاسماء الخمسة وتشمل :أب /أخ/فم/حم/ذو ..

الاسم يتغير طبقا لاعرابه :

يرفع بالواو

ينصب بالالف

يجر بالياء

(فيقال : اغسل فاك ( اعرابه منصوب لانه مفعول به فينصب بالالف 

(يخلو فوك من اي تسوس ( اعرابه خبر مرفوع بالواو

(قلت هذا بملء فيك ( وهو مضاف االيه مجرور بالياء

weyn bi2ulu 'fam'? smi3t bas 'tem' 'temmo' temmak'

I think it might be a typo. I've never heard that word before.

فاه = فم
synonymy
they both have the same meaning
فاه is more common in literature and poetry
فم is more common in everyday language and most of people use this word