I don't think your intention was to be "nasty". You are much too nice a fellow for that kind of behavior.
However, on a public bulletin board it is generally bad form to correct another poster's grammar or spelling. It can inhibit the conversation and the exchange of information and I know you wouldn't want that. No one likes to be corrected in public and while Terry took it with remarkable good grace another reader might be afraid to post for fear of not using the absolute correct language. So, it is best just not to do it.
I appreciate your understanding.
gail