Migrating shellfish

So apparently some Norwegians claim that our planet is warming up as evidenced by some migrating mussels. And of course, the story reporter, most likely a liberal, indicates that this is because of our polluting. Here is the ridiculous contradicting paragraph that completely rebuts their argument.

"It seems like the mussels we found are two to three years old," he told Reuters. Such shellfish have not been recorded off the islands since Viking times 1,000 years ago during another warm period.

Unless this reporter wants to argue that the vikings were cause of global warming 1000 years ago, this article is telling us that during a previous normal warm period of the earth there were mussels, but now this warm period where the same mussels are living in the same place can only be explained by global warming caused by our greenhouse emissions?

There are no actual quotes in the article of the Norwegians claiming that the warming is caused by our pollution, so I don't want to place this criticism on them. It's just the liberal spin that the reporter is throwing onto the story.