Somewhat accurate. What causes the eyestrain is the actual LEVEL of the effect initiated. It's got much less to do with how far away from the screen you are than the amount of 3D effect that's in place. For example, on a scale of 0-100, a 3D level of 25% causes your eyes to separate and stress less than a level of 75%. Regardless, if any technology causes impairment in more than an inconsequential amount of the population (say 0.5%), it shouldn't be utilized at all.
Besides, it's not even "3D", it's 2D with adjusted images that essentially amount to being out of focus.
I think you've misunderstood something. When 3D is properly set up, it doesn't force your eyes apart at all! When looking into infinity your eye convergence should be zero, i.e. looking straight ahead. So, if your eyes are (say) 3 inches apart, then the two images of a 3D object at apparent infinity on the screen should be 3 inches apart. For any object 'nearer' on the screen the two images should be closer together, causing your eyes to turn in
toward each other, which is what they do naturally when you're looking at close objects.
The forcing your eyes apart happens when a 3D sequence adjusted for (for example) a 20 foot screen is projected onto a 40 foot screen, doubling the 'infinity' separation from 3 inches to 6.
If 3D ever forces your eyes to diverge, then it is just flat out being done wrong!
And you're sort of right about the 'out of focus' but I suspect not in the way you mean. What is happening there is that the 3D effect is reproducing the convergence-of-gaze that gives us depth information over long distances, but because the images are properly focussed on the screen the lenses in our eyes (which give depth information over short distances) have to focus at the depth of the screen and not at the apparent depth of the 3D image.
This problem is in fact really severe if you're using a monitor, which you sit close to. If you're watching on a widescreen TV or a cinema screen then it's hardly a problem, as lens focus only really kicks in closer than about 10 foot.