man, the stingray was 1m WIDE, i'm fairly certain he could see it, if they're so unpredictable then why did he risk getting so close? its because they're not normally harmful and to be killed by one is probably less likely than winning devision 1 lottery.
Depends on a lot of things.
First, a ray is colored to be hard to see in the water.
Second, the tend to lay partially buried in sand.
Third, they can move quickly in the water.
A couple of years ago I was snokling off the keys in about 4 feet of water. I noticed a shadow below me. It was a Manta Ray, seemed like about 5 feet across, but in my surprise I can't be sure.
It came up behind me so smoothly I didn't notice it until is was starting to pass. Had it been a sting ray, I could easily have been in range of it's barb. All it would have had to do was notice me and panic.
I can see many ways that this could have happened without Steve provoking the animal.
They are now saying the he did not pull the barb out. Makes sense, it would have still been attached to the ray. They also say that people have been killing rays in retaliation.
I can think of no worse insult to what Mr Irwin devoted his life to, than to kill animals for no good reason.