The ethnic groups that make up the majority of Pakistan have a less than 5% representation among Indians. The same could probably be said for Bangladesh.
Not only that, but Pakistanis write in a Perso-Arabic script which Indians can't read, a lot of us speak languages Indians can't understand (e.g Pashto, Balochi and Hazaragi), we have far higher amounts of Eurasian ancestry, many Pakistani tribes/clans aren't present among Indians (Awans, Arains, Syeds, Ansaris, Qureshis, Bara, Mughals, etc) or exist in very small numbers (e.g Janjua, Waraich), we follow a different religion, our women wear more modest clothing, etc.
It's not bogus at all. Muslims and Hindus are completely different from one another for various reasons. Muslims can't and won't drink/eat from the same utensils as Hindus, we can't and won't marry Hindus, we have different heroes to Hindus, we have a different physical appearance to Hindus (skull caps, long beards, headscarves, no bindi, no sari, etc), we have a different diet to Hindus (we eat far more meat, especially beef), we pray in Arabic, we keep Persian, Arabic and Turkic names, we tend to write in a Perso-Arabic script, we heavily frown upon idolatry, etc. Not only that, but for most of history Muslims and Hindus just haven't gotten along. This is still the case today. Sure, there are some exceptions, but they're just that, exceptions, not the rule. If you don't believe me, go and ask a Muslim from India whether he is Muslim or Indian first. I can guarantee that most of them will say they're Muslim first, as is the case with Pakistanis and plenty of other Muslims:
View attachment 532054
The fact that Muslims are so different to other communities from what was British India as well as the fact that people from the Indus are also as a whole distinct from the rest of what was British India makes Pakistan's partition perfectly legitimate.