Issue in this reading comprehension passage - do subsequent statements counter the original statement?

This comprehension comes from a CBSE Paper, which is the final English Paper for Grade 12. I am selecting the paragraph from which the question is from.

I could not find the passage in text form, and so had to make do with a screenshot. The reference is this, and the original paper with the questions can be found here.

The question I have a problem with is as follows:

Why do we feel suffocated in a closed environment?

According to the answer key in my reference book, as well as the page which mentions this question, the answer is:

We feel suffocated in a closed environment due to a lack of oxygen.

According to me, this answer is incorrect, since the passage explicitly mentions that this is not the actual reason. The actual reason could be exposure to poisonous gases, for instance. This is substantiated by the fact that the author uses the word however in the next sentence.

So, my question is this - I am misinterpreting what the paragraph is saying? Or, is the question only referring to that particular sentence (which, in isolation, can be considered to be a fact presented by the author)?

And, more importantly, if the answer is wrong, then what should the correct answer be?

You are correct that there is an issue with the answer exactly as it's written.

There is a difference between feeling something to be the case, and something actually being the case.

In the passage, the key phrase is:

It is often ascribed to the lack of oxygen.

So, a more accurate answer (and interpretation of the text) would be:

We feel suffocated in a closed environment because we fear there is a lack of oxygen.

The rest of the passage goes on to say that this fear is often unfounded.