While the comment you replied to was "extreme", it is impossible for any muslim to not know the difference when the difference defines everything about how they practice their religion.
Are you muslim? In the real world most muslims are not that religious and hardly follow what is taught to perfect precision. They would not be able to answer the difference except in vague terms at best.
Every single muslim, whether devout, practicing, lapsed or whatever, knows whether they are/were Sunni or Shia. They are literally born into it. It determines who is seen as the authority in matters of their faith, the way they pray, the sites they consider holy, the religious days they observe. Even Ramadan starts and ends on different days depending on which you are.
It's such a fundamental thing that I question whether you have any idea about what you're saying here.
I don't know much about Islam, but what's being described isn't uncommon for lapsed Christians. I know plenty of people in my orbit (including me) who went to mass on Christmas Eve and Easter as children, but literally wouldn't be able to answer if the curch they went to was Catholic or Protestant.
The difference between Islam and Christianity on this is so stark that I am trying so hard to not respond in a rude manner and tell people to read a book or something.
It's like if you didn't know a single thing about Mandarin but insisted on making claims about its grammatical rules because you know English grammar.
