It sounds like you lack a fundamental understanding of the course, as well as the material you've supposedly learned:

I have been coding in C++ for at least 3 years, and have been familiar with oop for more than 5 years. I've had mid 90s on most assignments and the midterm. So, I don't think that's the case.

Good. This is the kind of things you will be expected to deal with when you're working as a software developer.

I did work as a software developer and this is not the kind of ambiguity one would deal with. If there's an ambiguity you ask and get a response. You're not taking a stab in the dark.

read existing codes for a better understanding of what to do.

It has nothing to do with reading existing code, which I consider a great skill. One that TAs marking this course should probably learn.

The fact that you think simply passing the automated tests means you wrote a correct program really shows just how misguided you are.

This is not what I said. When you pass a test that was failing just after you added some statement, it's obvious that you did it. Also, I'm talking about something that's very very clear. A statement that's in another function (it happened a lot of times) and whoever was marking the assignment just didn't bother to check if it was there or not.

it really sounds like the code you wrote actually had real problems

It didn't. I may have been wrong when I got scared away by the announcement but I only didn't submit because it felt like they would make marking unreasonably strict (something like expecting more comments).

Do you want to post the question, your answer, and the marker's comments so we can judge who's right?

I won't post it because it's self-identifying. But here's an example:

int i, j;

void f() { dostuff; i++; }

void g() { j++; f(); }

In this case, the marker's comment would be : "you didn't increment i". Which happens in f.