If it's a label, then it's not a disability.
But that doesn't mean they struggle for the same reasons. There is a huge difference between struggling because of a brain condition you were born with and "struggling" because you just don't put enough effort into something.
The NHS for example says all evidence points toward it being genetic so you may want to support your claim that other people can get the "label" and be called dyslexic for non-biological reasons. Or we can just move on and assume your claim is bollox.
He doesn't, he says the other people are not dyslexic even though you wrongfully slap that label onto them.