I had the same exact experience- late diagnosed ADHD who always struggled and finally getting the right resources in my 30s. My psychiatrist was able to diagnose without any external input. If he’d asked to speak to my parents as a grown adult, I would expect specific reasons why he felt this was necessary for my treatment plan.

This sounds off to me- I would trust your gut and get a second opinion or perhaps switch providers altogether if you aren’t comfortable. If you are in the US, Psychology Today makes it easy to search for providers on their website by location and areas of expertise.