I have many reasons for disliking the Scottish Greens in general and Wightman in particular; none of them are silly.
I'm not a Holyrood "wonk", whatever that might be. Wightman is the author of 2 very successful books (Who owns Scotland and The Poor have No Lawyers) both of which are permanently on display in the Scottish section of Waterstones. I think anyone with even a smattering of interest in Scottish politics would have come across him.
I don't recall him expressing any particular interest in , or speaking about, green issues. The wilder fringes of the SNP would be a more natural fit but I suppose Sturgeon wouldn't want him.