I think you're misreading an opinionated statement as being a literal statement of fact.
I saw an answer on SO which said that just having a class with methods doesn't make it OOP and that it represents Class Oriented Design.
If I really like cars, and I have a distaste for cheap foreign vehicles, I could tell my friend who drives a cheap foreign car "just because it has four wheels and an engine doesn't make it a car, you know", and then my friend then takes this as truth and goes around looking for an answer to what the definition of a car is.
This is the position you find yourself in. You took what you heard as the literal truth and are now on a search for the answer that confirms what you heard.
What you heard wasn't literal truth. It is known as the "No True Scotsman" fallacy, whereby the speaker argues that a commonly understood definition, i.e. Scotsman, should be applied more restrictively. Instead of "person from Scotland", the speaker argues it should be "person from Scotland who doesn't put sugar on his porridge".
The problem here is that the speaker willfully redefines a commonly understood concept just to argue their point. While their underlying point may or may not be valid, silently changing definitions is a sign of poor communication skills as it does nothing but add confusion, just to not have to acknowledge something you don't like (such as sugar on your porridge, I guess).
The same is happening here. (Non-static) classes lie at the base of OOP design. However, the speaker is arguing that one can still use classes badly, and therefore such bad usage is "not true OOP". I don't quite disagree with their underlying argument, but I disagree with their conclusion and how they try to label it.
I'm not saying he's wrong per se, there is merit to his argument, but he's trying to argue about a purer form of OOP and is wrongly calling everything else "not OOP", instead of admitting it's "just not very pure OOP". It's at the very least an overstatement, which sadly detracts from the value of the underlying opinion which may actually contain value.
That being said, I'm not going to claim that I've never pulled a "no true ..." claim, but I'd like to think that I only do so when it is clear that I'm expressing a personal opinion rather than an objective truth, so it is clear that I'm talking about a personal definition rather than a common one.
Feel free to correct me if I'm wrong, but based on your question/comments I surmise you are a beginner who is learning about OOP. It's good that you're trying to think critically about what others say, but beware taking things too literally.
The internet is filled with people who tout personal opinion as if it were objective fact, and especially in abstract fields such as software development, it's easy to be misled by someone's assertions.