It's wonderful how people attack the "spelling" police. The earlier you have pointed out to you that spelling is important the better. Why? Because if you submit a job application with spelling (or grammar) mistakes in it it will be one of the first in the bin as it shows unprofessionalism and lack of care.
Just take it on the chin. They are actually trying to help you - even if it's not obvious and they are a bit rude about it.