Actually?  Yes, it is.

Now...if we go back to the Urban Dictionary, we will see "Yup is a generic term of agreement issued often by a non-listening party, typically used while performing an additional important task, such as watching tv. "

But...it IS recognized by both Oxford and the more common Webster dictionaries....as your "idear" is not.

Any more aspersions you'd like to  cast on my education, degrees, or comprehension?