OCD being mistaken for ADHD

Someone close to me is on their journey to discover what is going on in their brain. OCD is finally making the most sense and explains a lot, so they are accepting that. But they are still trying to pursue an ADHD diagnosis, even when the OCD is the culprit and can cause some very similar symptoms. They are convincing themselves they have it, even though they admit they had none of the symptoms present in childhood (a requisite for ADHD diagnosis), they only showed up in the last year when their OCD started getting more intense. They have also had a negative screening 2 or 3 times.

Any similar experiences here? And how can I help them see the ADHD is not the answer and not make it seem like I’m gatekeeping the disorder?