T'weren't a typo. A typo is a misspelling. This was a problem of word choice. Rule of thumb: if you don't know the actual phrase, don't use it. For example, how often have you read "he would of" when the writer meant to say "he would have." Simply because we hear something one way does not mean that is the way it is written.
Of course you are right, but that doesn't mean the writer doesn't say it properly, or know what he meant to say.. All I can say, is that sometime in haste, the eye sees the word spelled properly, without reading the context of the sentence.
Not to quibble, but really, it's not fair for a poster to refer to him as a halfwit because of one word. Seems a little Dan Ratherish to me. Hehehe. For I can spell, therefore I am smarter and better than you.. Uh huh.. sorry.. fails the smell test.