Let's settle this question, that why Punjabi Muslims from East Punjab are not called Muhajirs and people coming from UP/CP are called Muhajirs?
First and foremost, Punjab was/is one province, which was artificially divided by drawing a border, so people from one province, who had to move to the other side of the same province because of the line is drawn by Redcliff for the sake of division cannot be called Muhajirs but people displaced in their own province by the artificial division for the sake of partition.
They have everything in common except religion, which did not matter a lot, as Punjabis are secular people first, their Muslim identity has been recently crafted and it became problem in Pakistani Punjab, as in the absence of collective Punjabi identity and culture, they were left wondering about their heritage, which partition suddenly took away. In this confusion, they were imposed with alien language and culture.
Both parts ofPunjab are still linked by land, which is not the case in UP/CP people, their provinces are not linked by land to territories of Pakistan.
So, people hailing from the same province, just moving to the other side of the province due to religious killing cannot be termed as Muhajirs, but people, who had come from areas not linking with territories of Pakistan are defined legally correct as Muhajir.
The Punjabis moved in their own province rather to new areas like UP/CP.
Secondly, it is Altaf Hussain and MQM, which started calling them Muhajirs though correctly.
If UP was partitioned and people moved in the province from one side to another, they would not be called as Muhajirs. So is the case with Punjabis.