He invented the optical mouse, among other things. He has no education or background in medicine or the biological sciences, and it shows.
Substack is a legit forum for newsmen and bloggers to express their views.
Some are more legit than others but there is no reason to dis them just because they use a substack rather than Wordpress.
Keep in mind - one of the patent holders of the optical mouse is a FReeper who worked for Xerox PARC.