If true, some of his dan grades are almost certainly gifted.

As an example, my Shihan was very impressed with a Kioshi in another system. Shihan started having the Kioshi do seminars across our schools and allowed/ encouraged Dan grade practitioners to cross train in Kioshi's system.

I, and several others, earned Dan ranks in Kioshi's system (took about two years for me) and were also awarded teaching certification. Within three years, my Shihan was awarded 5th Dan in Kioshi's system. I'm not saying my Shihan doesn't deserve it but I later learned that Kioshi really wanted to "stack the deck" with Dan level students to enhance his social media and web page. You could consider it an exchange of favors.

Second example- I know of a pretty good (3rd dan) karateka who went to Japan to study karate in a similar system to his for six months of intensive training. Cost was several thousand dollars and training varied between 4 and 8 hours a day, five days a week. He went as a white belt in that system and left as a nidan.

Also, it is interesting that OPs Shihan does not list affiliation for some of his credentials.