"What's wrong with your kid?" What responses do you give?

I had this negative interaction a few weeks ago and it really got me thinking about how to handle explaining my son to others (that frankly have no business in our lives) what is indeed noticeably different with my son.

I was buying balloons for my boys and Chase my little SPD wonder was actually behaving really, really well. I was so proud of him. He was on his monkey leash and his gross motor skills are awkward and his speech is delayed, so I'm sure he was looking a bit remarkable. The sales lady asked, "what does he have?" I honestly thought she was talking about the monkey leash so I sort of stood back from him [thinking: get an eye full lady]. But then she clarified, "does he have autism?" well he doesn't, but he does have SPD and perhaps other things yet TBD. Anyway, I asked lots of people, what should I say? I don't want Chase to be defined by SPD. While I'm pretty cool embracing it as a component of his life, it is not the only factor by which I'd like to describe him.

My father suggested the answer, "He is the gift of patience" and I've since decided that pretty much summed my sweet boy up.

But how do you get around talking plainly about the truth without sounding insulting? You know you're having the conversation with the mom sitting next to you at T-ball or at school pick-up... these things just come up. I super up-front about our struggles and successes without little ears around, but with Chase right there... I just hate having conversations about him, in front of him.

What lines have you used?
How much do curious strangers deserve to know?