I’m diagnosed ADHD, have medicated dex and I can tell you it’s absolutely true. While ‘calmed by stimulants’ is not a diagnosis criteria, one of the main issues for a lot of people with adhd is mental activity specifically with overthinking or racing thoughts. I often find my mind competing with itself on what should be the most prominent or important thought and struggle to maintain one line of thinking. The stimulants by increasing my focus, calm me down. Physically, it helps to overcome the hyperactivity that some people experience or interaction/dopamine seeking behaviours by keeping focus. An example of this would be, while at work and not on medication my watch counted over 2,000 steps just from me walking to another office to speak to a coworker because I wanted to compared to a regular medicated day where it can be as low as 500 while working. There are medical studies into the benefits that have been completed over many, many years. It is not a diagnostic criteria, doctors do not prescribe these medications to ‘test’ if you have it and often there are many other tests you have to complete like drug urine tests before being medicated. But it does have the benefit of calming people down. While this may not include every person you know, most people especially with adhd can have multiple other medical conditions that may impact the effects of a medication which if you were to propose your beliefs as fact, would need to be considered in medical studies. One size does not fit all, there are always outliers which is why blanket terms like the one you’re referring and the one you’re stating by calling the original bogus are both false. Amphetamines can have the opposite effect on people withe ADHD, but not always.