I agree with one and all - those remarks are totally out of line! And especially with Minnie's comment about showing your child what is a good/correct reaction to this kind of thing, even if it took a while for you to sort your reaction.
Unfortunately this might not be the only time he and you have to deal with such negative remarks intended clearly to "take him down a peg". Which is, of course, ridiculous.
The lack of warning is especially bizarre! I guess these are her real feelings, but it certainly makes you wonder why she got in to gifted work at all...maybe this if the first time she's encountered a student really off the usual charts?
Sorry to hear about the problems, but you are in the right, she is wrong and she's messing up your kid
. I definitely think it's 'time to make a bloody hell'.