This isn't really an answer to the question...but was too long for a comment.
In general, I am told I tend to overshare personal information, so take my comment with a grain of salt.
If I were in the OP's position, I would provide a response to the best of my ability (using the interpretations suggested by commenters above).
However, I would also include something along these lines in my response: "I believe that my attached response answers your question, but I have to admit that I am still a bit unsure that I interpreted the question correctly. As an employee, when I face this type of situation, I will go back to the original questioner and ask for clarification, but that was not an option in this situation. So, if you review my response and it seems completely unrelated to the question, please allow me to get further clarification about what you would like to know, and I will be happy to respond again."
I think the OP is completely within his rights to pursue this position, even if his English isn't perfect. But, the best way to turn a potential negative into a positive is not to try and cover it up and hope the employer doesn't notice, but to proactively address the issue up front. He acknowledges that his English is not as good as a native speakers, but at the same time he reassures the employer that he himself is aware of the issue and that he already has a solution for it.
I was once fired from a job, ostensibly because I missed a particular deadline, but really because the office management had changed and the new person in charge didn't like me, and took this as an opportunity to fire me.
On interviews for a new position, I would always try to address this firing before the interviewer even asked why I had left the other company. I explained that I had been put into a position where I was guaranteed to fail at one of my responsibilities--either missing the deadline, or letting a team go out to an interview without proper preparation, and I made a judgement call. I explained that my direct supervisor and I had discussed it afterwards and had figured out how we could avoid a similar situation in the future, and then I explained that the deadline was important enough to upper level management that someone had to be a scapegoat, and I ended up being that person.
I went on four interviews before accepting a new job, and each of the people that interviewed me gave me really positive feedback about my being forthcoming with this information.