So he probably answered exam questions written by the Scottish universities but whilst he was studying in Durham university.
Probably not. I think the professors at Durham would have been perfectly capable of writing their own exam questions for their own undergraduates.
There was always a lot of exchanging of ideas and new technologies among postgraduates and academics, but by and large, undergraduates didn't chop and change from one university to another, and there was nothing like the student exchanges that are on offer now.
Also I don't think there would have been much undergraduate mixing between the Scottish universities and Durham. Even when I was an undergraduate student at Edinburgh in the 1960s we didn't really have anything to do academically with any other Scottish universities, let alone Durham or anywhere else.
You signed up for your three-year ordinary or four-year honours or five-year dental or six-year medical degree, and you either stayed the course or dropped out altogether. Modern languages honours students went to spend a year at a university in a country where their principal language was spoken (unless it was Russian or Chinese and possibly some others where it wasn't possible, or a dead language like ancient Greek or Latin or Sanskrit) but everyone else stayed put for the duration until they got their first degree. Then they might go on to further study somewhere else, for example my uncle graduated in medicine at Edinburgh and went on to further study at Oxford.