Wales vote was 854K to 772K, so if you analyse it out:There you go.
https://nation.cymru/news/wales-brexit-vote-caused-by-english-retirees-oxford-university/
Any other lies you want evidence about?
Around 650,000 of the people living in Wales were born in the UK (number from his paper), so if they voted the same as Cornwall (57/43) (the most pro Brexit region) and you adjust for turnout (71% in Wales) they would have still voted Brexit. (change is 65,000 votes) This includes people who moved there are children and no doubt identify as Welsh, and assumes none of the 650,000 are children. So he might not be right.
Looking at what he has written there is a thin line between politics and geography there days. Nothing about oxbow lakes in his stuff.