I think it's natural to feel somehow embarrassed (or is it the culture we live in?). Anyhow. Don't feel bad for yourself. I sometimes feel the same - we do make mistakes but when someone finds a bug and reports it, try feeling good about it. The person took some time to read your code and even spend time to write you that something could be improved.
Tom McFarlin (known as WordPress developer) wrote a nice article about that "This could be better".
One last word about the tone. Keep calm. You don't know what this person has gone thru today. Maybe s/he had a rough day. If the person repeatedly uses that tone you should ask her/him why.