Basically, it's the same sort of difference between test that shows you may be likely, based on your genes, to get cancer and a test that shows you actually have cancer.  

Some of this has faded from my memory banks, but my recollection is that two noted doctors (including the guy who told Reggie Lewis he shouldn't be playing) actually looked at his heart and cleared him to play.

Thus, the situation for Curry was this. He had two noted doctors look at him and say his heart wasn't abnormally enlarged and he was fine to play.

He had a third doctor say in effect "ok, but you could also get this DNA test to see if you're genetically predisposed to having this condition which you've been told you don't actually have".

The Bulls made their contract offer conditional upon passing the test and showing he wasn't "predisposed" to the condition, not whether he had the condition or not.  

Since I'm on my soapbox, one thing I always thought was incredibly lame was that if he turned out predisposed, then he got a parting gift of, effectively, his the present value of his "qualifying offer" amount spread over the course of something like 20 years.  That sounds pretty nice (and was talked up as a "compassionate" solution by guys like KC) but the reality was it was little more than what he could have had anyway since they'd already tendered him that amount.  

That is, the Bulls made themselves sound compassionate by offering to spread the money they'd already agreed to pay in one year over 20 or 30 years with interest.

That, of course, made the number sound bigger, but probably reduced the real value.  It's a little more irritating in the context of them paying Jay Williams significantly more than that (they basically let him collect his salary for two years) when he wrecked himself.  I mean, I don't really begrudge the Bulls doing that for Williams (it was good PR on their part in that case as well), but it's pretty hard for me to justify giving more to a guy (Williams) who wrecked his career in an act of stupidity after having done nothing in one season for you than to a guy (Curry), who you're forcing to take a test that doesn't actually prove he's sick, and who (despite obvious flaws) had actually helped you win games on the court.

The whole affair left a pretty bad taste in my mouth.