On the same page 13 I think you missed THIS bit..
** *The majority of those who had migrated to West Punjab (Pakistan) had
moved from East Punjab (India). As such there was no problem at the level
of culture or language and hence, integration.***
The point is both you and Aliyish are right, Aliyish is refering to URDU SPEAKING immigrants from UP, CP and other areas of India (Generally THEY are refered as MUHAJIRS), and MAJORITY of them migrated to Sindh. If we include Punjabi Speaking migrants, then total of course comes around 70% of mass migration.
Can't get much simpler then this. However, its obviously a known fact, but people are acting naive and playing petty arguments around it.