There is the kernel of a truth underlying their thinking - for a given dose of stimulant, someone without ADHD is more likely to feel overstimulated than is someone with ADHD. But the range of individual variation, both within those with ADHD, and within "neurotypicals" is so great, that you simply can't use one person's response to one dose of a stimulant to diagnose somebody.

But I'm glad that you have found something that works well for you!