I'm sorry it hit a nerve with you. You're obviously still feeling a bit raw.
Even though I could see it for myself, I was a little bit sensitive about some of the things said about DS1 when he was first being diagnosed, partly because i took them to be a reflection of my own parenting, since no one had conformed that he was autistic and hyperactive rather than badly disciplined at that point. Other things I'd already reached the point of black humour with.
It might not have been meant in a derogatory way, anyhow. There's a constant rolling tape on the TV screen in the reception area of DS1's school and part of it is footage of some "Expochef" visit from last year. DS1 was in reception, then, so in the front row, right in front of the camera and I've actually commented, myself, to his TA that he's fascinating to watch. He's being totally himself (at the time it was filmed), so a bit fidgetty, but he's so animated and occasionally, he responds so enthusiastically to something that happens out front, then he drifts off into the land of his own thoughts again.
And I agree with Goblinchild, that it's helpful that they are noticing that he is different. The school will be asked for their views at some point in the assessment, and again if you apply for DLA, if you haven't already. If you receive comments like "he's so fascinating" in the future, politely ask whoever says it for a clarification, since those are the opinions they'll be likely to be sharing and which will, hopefully, go some way to building up a picture of why your son was referred for assessment in the first place.