That article is only speculation, just as your opinion is. They claim the possibility of several reasons for the limit on the S9 before only discussing heat as a possibility, not as fact. They never discussed the other possibilities (whatever those may be, they didn't say), and they also pointed out that Samsung did not respond to a request for more information on why the limit is there.
And it is a fact that as technology advances, it's very possible for a faster processor to run cooler doing the same work as a slower/older one. If heat were the issue, then I would expect the limit to be based on that, recording as long as the system can handle it before the temps become an issue. An arbitrary set time limit doesn't sound logical when you can immediately restart the recording without a cool down period.