The only thing Yngve Slyngstad is doing is buying or selling stocks. What he does has no impact on the economy. So his opinion is not relevant.
BMW on the other hand, has economical activities in the UK. They invest, import, export, create jobs, pay taxes... So while they are far smaller then the Norwegian pensionfund, their impact will be 100 times more important for the UK. If they leave the Uk will lose thousands of jobs. If Yngve Slyngstad leaves, by selling stocks, other investors will buy these stocks. So that will have no impact at all on the UK economy.
They interviewed the wrong person.